Halacha

הלכה א
הָאוֹמֵר זֶה בְּנִי אוֹ זֶה אָחִי אוֹ זֶה אֲחִי אָבִי אוֹ שְׁאָר הַיּוֹרְשִׁין אוֹתוֹ. אַף עַל פִּי שֶׁהוֹדָה בַּאֲנָשִׁים שֶׁאֵינָן מֻחְזָקִין שֶׁהֵן קְרוֹבָיו הֲרֵי זֶה נֶאֱמָן וְיִירָשֶׁנּוּ בֵּין שֶׁאָמַר כְּשֶׁהוּא בָּרִיא בֵּין שֶׁאָמַר כְּשֶׁהוּא שְׁכִיב מֵרַע. אֲפִלּוּ נִשְׁתַּתֵּק וְכָתַב בִּכְתַב יָדוֹ שֶׁזֶּה יוֹרְשׁוֹ בּוֹדְקִין אוֹתוֹ כְּדֶרֶךְ שֶׁבּוֹדְקִין לְגִטִּין:
כסף משנה
1.
When a person says: "This is my son," "This is my brother," "This is my uncle," or identifies a person as any of his other heirs, his word is accepted and that person inherits his estate. This applies even when he makes this acknowledgment concerning people who are not recognized to be his relatives. And it applies whether he made such a statement when he was healthy or when he is on his deathbed. Even if he lost his power of speech and identified a person as his heir in writing, his word is accepted, provided we test his powers of understanding as we test a man with regard to divorce.

הלכה ב
הָיִינוּ מֻחְזָקִין בָּזֶה שֶׁהוּא אָחִיו אוֹ בֶּן דּוֹדוֹ וְאָמַר אֵינוֹ אָחִי וְאֵינוֹ בֶּן דּוֹדִי אֵינוֹ נֶאֱמָן. אֲבָל נֶאֱמָן הוּא עַל מִי שֶׁהֻחְזַק שֶׁהוּא בְּנוֹ לוֹמַר אֵינוֹ בְּנִי וְלֹא יִירָשֶׁנּוּ. וְיֵרָאֶה לִי שֶׁאֲפִלּוּ הָיוּ לַבֵּן בָּנִים אַף עַל פִּי שֶׁאֵינוֹ נֶאֱמָן עָלָיו לוֹמַר אֵינוֹ בְּנִי לְעִנְיַן יִחוּס וְאֵין מַחֲזִיקִין אוֹתוֹ מַמְזֵר עַל פִּיו. נֶאֱמָן הוּא לְעִנְיַן יְרֻשָּׁה וְלֹא יִירָשֶׁנּוּ:
כסף משנה
2.
When one person is recognized to be another person's brother or cousin, and the latter says: "He is not my brother," or "He is not my cousin," his word is not accepted. His word is accepted, however, with regard to a person who is recognized to be his son. If he says he is not his son, he does not inherit his estate.
It appears to me that even if the son already fathered children - although at that point, the father's word is no longer acceptable with regard to the determination of his lineage, and we do not consider him a mamzer because of his father's statement - his father's word is, nevertheless, accepted with regard to the concept of inheritance. He should not inherit his father's estate.

הלכה ג
הָאוֹמֵר זֶה בְּנִי וְחָזַר וְאָמַר עַבְדִּי הוּא אֵינוֹ נֶאֱמָן. אָמַר עַבְדִּי וְחָזַר וְאָמַר בְּנִי אַף עַל פִּי שֶׁהוּא מְשַׁמְּשׁוֹ כְּעֶבֶד נֶאֱמָן שֶׁזֶּה שֶׁאָמַר עַבְדִּי כְּלוֹמַר שֶׁהוּא לִי כְּעֶבֶד. וְאִם הָיוּ קוֹרִין לוֹ עֶבֶד בֶּן מֵאָה זוּז וְכַיּוֹצֵא בִּדְבָרִים אֵלּוּ שֶׁאֵין אוֹמְרִין אוֹתָן בְּיִחוּד אֶלָּא לַעֲבָדִים הֲרֵי זֶה אֵינוֹ נֶאֱמָן:
כסף משנה
3.
When a person states: "This is my son," and afterwards, says: "He is my servant," his latter statement is not accepted.
If he states: "He is my servant," and afterwards, says: "He is my son," his latter statement is accepted. This applies even though the "son" serves him like a servant. We interpret his statement that he is his servant to mean that he relies on him like a servant. Nevertheless, if people would call this individual "A slave worth 100 zuz" or the like - i.e., expressions that are appropriate only for servants - the deceased's retraction is not accepted.

הלכה ד
הָיָה עוֹבֵר עַל בֵּית הַמֶּכֶס וְאָמַר בְּנִי הוּא זֶה וְחָזַר אַחַר כָּךְ וְאָמַר עַבְדִּי נֶאֱמָן. שֶׁלֹּא אָמַר בְּנִי אֶלָּא לְהַבְרִיחַ מִן הַמֶּכֶס. אָמַר בְּבֵית הַמּוֹכֵס עַבְדִּי הוּא וְחָזַר וְאָמַר בְּנִי הוּא אֵינוֹ נֶאֱמָן:
כסף משנה
4.
If a person had to pass through customs and identified an individual as his son, but afterwards identified him as a servant, his later statement is accepted. We assume that he identified him as his son only to avoid paying customs duty. If, however, in customs, he identified a person as his servant, and afterwards identified him as his son, his word is not accepted.

הלכה ה
הָעֲבָדִים וְהַשְּׁפָחוֹת אֵין קוֹרִין לָהֶן אַבָּא פְּלוֹנִי וְאִמָּא פְּלוֹנִית שֶׁלֹּא יָבוֹא מִן הַדָּבָר תַּקָּלָה וְנִמְצָא זֶה הַבֵּן נִפְגָּם. לְפִיכָךְ אִם הָיוּ הָעֲבָדִים וְהַשְּׁפָחוֹת חֲשׁוּבִין בְּיוֹתֵר וְיֵשׁ לָהֶן קוֹל וְכָל הַקָּהָל מַכִּירִין אוֹתָן וְאֶת בְּנֵי וְעַבְדֵי אֲדוֹנֵיהֶם כְּגוֹן עַבְדֵי הַנָּשִׂיא הֲרֵי אֵלּוּ מֻתָּר לִקְרוֹת לָהֶן אַבָּא וְאִמָּא:
כסף משנה
5.
A person should not call a servant Papa Joe or a maidservant Mama Sarah lest this lead to an undesirable outcome and a blemish be placed on his lineage. Therefore, if there were servants or maidservants who were very distinguished personages, their reputations are well known, and everyone in the community recognizes them and the children and servants of their master - e.g., the servants of the nasi - it is permitted for the children of that household to refer to the servants in the above manner.

הלכה ו
מִי שֶׁהָיְתָה לוֹ שִׁפְחָה וְהוֹלִיד מִמֶּנָּה בֵּן וְהָיָה נוֹהֵג בּוֹ מִנְהַג בָּנִים. אוֹ שֶׁאָמַר בְּנִי הוּא וּמְשֻׁחְרֶרֶת הִיא אִמּוֹ. אִם תַּלְמִיד חָכָם הוּא אוֹ אָדָם כָּשֵׁר שֶׁהוּא בָּדוּק בְּדִקְדוּקֵי מִצְוֹת הֲרֵי זֶה יִירָשֶׁנּוּ. וְאַף עַל פִּי כֵן אֵינוֹ נוֹשֵׂא בַּת יִשְׂרָאֵל עַד שֶׁיָּבִיא רְאָיָה שֶׁנִּשְׁתַּחְרְרָה אִמּוֹ וְאַחַר כָּךְ יָלְדָה שֶׁהֲרֵי הֻחְזְקָה שִׁפְחָה בְּפָנֵינוּ. וְאִם מִשְּׁאָר הֶדְיוֹטוֹת הוּא וְאֵין צָרִיךְ לוֹמַר אִם הָיָה מִן הַמַּפְקִירִין עַצְמָן לְכָךְ הֲרֵי זֶה בְּחֶזְקַת עֶבֶד לְכָל דָּבָר וְאֶחָיו מֵאָבִיו מוֹכְרִין אוֹתוֹ. וְאִם אֵין לְאָבִיו בֵּן חוּץ מִמֶּנּוּ אֵשֶׁת אָבִיו מִתְיַבֶּמֶת. וְזֶה הוּא הַדִּין שֶׁיֵּרָאֶה לִי שֶׁהוּא הוֹלֵךְ עַל עִקְּרֵי הַקַּבָּלָה. וְיֵשׁ מִי שֶׁלֹּא חִלֵּק בֵּין כְּשֵׁרִים לִשְׁאָר הָעָם אֶלָּא לְעִנְיָן שֶׁלֹּא יִמְכְּרוּהוּ אֶחָיו בִּלְבַד. וְיֵשׁ מִי שֶׁהוֹרָה שֶׁאֲפִלּוּ לְיָרְשׁוֹ לֹא נַחְלֹק בְּיִשְׂרָאֵל וְאֵין רָאוּי לִסְמֹךְ עַל דָּבָר זֶה:
כסף משנה
6.
The following rules apply when a person had a maidservant and fathered a son with her, and he would treat the son as one treats a son or said: "He is my son and his mother was freed." If the person involved is a Torah scholar or an honorable person whose conduct has been scrutinized and he is found to be precise in the observance of the details of the mitzvot, the "son" may share in the inheritance of his estate. Nevertheless, this "son" may not marry a Jewish woman until he brings proof that his mother was freed before she gave birth. The rationale for this stringency is that it has been established for us that the woman is a maidservant. If the person is one of the ordinary people - and needless to say, if he is one of those who act loosely in this manner - the "son" is presumed to be a servant with regard to all matters. His paternal brothers may sell him. If his father does not have any children other than him, the father's wife must undergo the rite of yibbum.
This is the law as it appears to me, for it follows the fundamental principles of the received tradition. There are, however, authorities who do not make a distinction between honorable people and people at large, except with regard to the ruling that his brothers may not sell him. ' And there are others who rule that this "son" may even inherit his father's estate, so that a distinction is not made with regard to Jews. It is not appropriate to rely on this ruling.

הלכה ז
כָּל הַיּוֹרְשִׁין יוֹרְשִׁין בַּחֲזָקָה. כֵּיצַד. עֵדִים שֶׁהֵעִידוּ שֶׁזֶּה מֻחְזָק לָנוּ שֶׁהוּא בְּנוֹ שֶׁל פְּלוֹנִי אוֹ אָחִיו. אַף עַל פִּי שֶׁאֵינָן עֵדֵי יִחוּס וְלֹא יָדְעוּ אֲמִתַּת הַיּוּחֲסִין הֲרֵי אֵלּוּ יוֹרְשִׁין בְּעֵדוּת זוֹ:
כסף משנה
7.
All the heirs may inherit on the basis of the prevailing presumption that they are the deceased relatives. What is implied? When witnesses testify that the prevailing presumption is that a person is an individual's son or his brother, the former may inherit the latter's estate on the basis of this testimony, even though the witnesses do not testify concerning the person's lineage, nor do they possess indubitable knowledge concerning his lineage.

הלכה ח
יַעֲקֹב שֶׁמֵּת וְהִנִּיחַ רְאוּבֵן וְשִׁמְעוֹן וְלֹא הֻחְזַק לוֹ בֵּן אֶלָּא שְׁנֵיהֶם. תָּפַס רְאוּבֵן לֵוִי מִן הַשּׁוּק וְאָמַר גַּם זֶה אָחִינוּ הוּא וְשִׁמְעוֹן אוֹמֵר אֵינִי יוֹדֵעַ. הֲרֵי שִׁמְעוֹן נוֹטֵל חֲצִי הַמָּמוֹן וּרְאוּבֵן שְׁלִישׁ שֶׁהֲרֵי הוֹדָה שֶׁהֵם שְׁלֹשָׁה אַחִין וְלֵוִי נוֹטֵל שְׁתוּת. מֵת לֵוִי יַחְזֹר הַשְּׁתוּת לִרְאוּבֵן. נָפְלוּ לְלֵוִי נְכָסִים אֲחֵרִים יַחְלְקוּ אוֹתָן רְאוּבֵן וְשִׁמְעוֹן שֶׁהֲרֵי רְאוּבֵן מוֹדֶה לְשִׁמְעוֹן שֶׁלֵּוִי זֶה אֲחִיהֶן. הִשְׁבִּיחַ הַשְּׁתוּת מֵאֵלָיו וְאַחַר כָּךְ מֵת לֵוִי. אִם שֶׁבַח מַגִּיעַ לַכְּתֵפַיִם הוּא כְּגוֹן עֲנָבִים שֶׁהִגִּיעוּ לְהִבָּצֵר. הֲרֵי הַשֶּׁבַח הַזֶּה כִּנְכָסִים שֶׁנָּפְלוּ לוֹ מֵאֲחֵרִים וְיַחְלְקוּ בָּהֶן. וְאִם עֲדַיִן לֹא הִגִּיעוּ לְהִבָּצֵר הֲרֵי הֵן שֶׁל רְאוּבֵן לְבַדּוֹ. אָמַר שִׁמְעוֹן אֵין לֵוִי זֶה אָחִי וְנָטַל לֵוִי בְּחֵלֶק רְאוּבֵן כְּמוֹ שֶׁבֵּאַרְנוּ וְאַחַר כָּךְ מֵת לֵוִי לֹא יִירַשׁ שִׁמְעוֹן מִמֶּנּוּ כְּלוּם אֶלָּא רְאוּבֵן לְבַדּוֹ יִירַשׁ הַשְּׁתוּת עִם שְׁאָר נְכָסִים אֲחֵרִים שֶׁהִנִּיחַ לֵוִי. וְהוּא הַדִּין בְּכָל הַיּוֹרְשִׁין שֶׁיּוֹדוּ מִקְצָתָן בְּיוֹרְשִׁין אֲחֵרִים שֶׁלֹּא יוֹדוּ מִקְצָתָן:
כסף משנה
8.
A person's statements regarding his relatives affect his share of an inheritance, but not that of his brothers. To illustrate by example: Jacob died and left two sons: Reuven and Shimon. The prevailing presumption was that he did not have any sons other than these two.
Reuven took Levi from among people at large and said: "He is also our brother." Shimon replied: "I don't know." Shimon is granted half the estate. Reuven is given a third, for he acknowledged that they are three brothers, and Levi is given a sixth.
If Levi dies, that sixth is returned to Reuven. If other property had been acquired by Levi, it should be divided between Reuven and Shimon, for Reuven acknowledges Shimon's claim to a portion of the estate, because Levi is their brother.
Different rules apply if the sixth that Levi was given increased in value on its own accord and then Levi died. If the increase were crops that were almost ready to be reaped - e.g., grapes that are ready to be harvested - they are considered to be property acquired from others and should be divided among the two brothers. If they are not ready to be reaped, they belong to Reuven alone.
If Shimon said explicitly: "Levi is not my brother," and Levi received part of Reuven's share, as explained above, and then died, Shimon should not inherit any part of his estate. Instead, Reuven should inherit both the sixth from his share and any other property that Levi left. These principles apply with regard to any other heirs when a portion of them acknowledge the existence of other heirs that the remaining portion do not acknowledge.

משפטים הלכות נחלות פרק ד
Mishpatim Nahalos Chapter 4