Yaakov has two sons, Reuven and Shimon. When Reuven dies and Shimon takes his wife in Yibum, he inherits Reuven, so Shimon gets a double portion from Yaakov's estate, his and Reuven's. What happens if Reuven is a Bechor who is entitled to a double portion, does Shimon get that double portion when he is MiYabem Reuven's wife?
3 Answers
The Maharshal in ים של שלמה in Perek 4, Siman 23 says that the Ramabam, the Ramban, the Rashba and the Tur all hold that he would not get a double portion, however Rashi and the R"I hold that he would. He himself sides with Rashi and offers a novel approach to the sugya in Yavamos Daf 40A.
The Korban Nesanel Yevamos 40A Number 20 brings it down as well, that the Maharshal holds that he would get the double portion.
If Reuven dies before his father then the Rambam says that he does not - since the father's inheritance would be "an added-value" after Shimon's death
מִי שֶׁיִּבֵּם אֵשֶׁת אָחִיו הוּא יוֹרֵשׁ כָּל נִכְסֵי אֶחָיו הַמֻּחְזָקִים. וְכָל הָרְאוּיִין לָבוֹא לְאַחַר מִכָּאן הֲרֵי הוּא בָּהֶן כְּכָל הָאַחִים שֶׁהֲרֵי בְּכוֹר קָרָא אוֹתוֹ הַכָּתוּב שֶׁנֶּאֱמַר (דברים כה ו) "וְהָיָה הַבְּכוֹר אֲשֶׁר תֵּלֵד יָקוּם עַל שֵׁם אָחִיו הַמֵּת וְלֹא יִמָּחֶה שְׁמוֹ מִיִּשְׂרָאֵל". וּכְשֵׁם שֶׁאֵינוֹ נוֹטֵל מִמֶּנּוּ בְּרָאוּי כִּבְמֻחְזָק כָּךְ אֵינוֹ נוֹטֵל בַּשֶּׁבַח שֶׁשָּׁבְחוּ נְכָסִים אַחֲרֵי מוֹת אָבִיו מִשְּׁעַת מִיתָה עַד שְׁעַת חֲלוּקָתוֹ עִם אֶחָיו בְּנִכְסֵי אָבִיו. וַאֲפִלּוּ הִשְׁבִּיחוּ נְכָסִים אַחַר שֶׁיִּבֵּם וְקֹדֶם שֶׁיַּחְלְקוּ הֲרֵי הוּא בַּשֶּׁבַח כְּאֶחָד מִן הָאַחִין. אַף עַל פִּי שֶׁנּוֹטֵל מִן הַנְּכָסִים אֵלּוּ שְׁנֵי חֲלָקִים חֶלְקוֹ וְחֵלֶק אָחִיו שֶׁיִּבֵּם אִשְׁתּוֹ הוֹאִיל וּמֵת הָאָב בְּחַיֵּי כֻּלָּן:
If the father died before Reuven, it seems that his double-portion goes to Shimon.
Someone pointed out to me over Yom Tov that the Korban Nesanal on the Rosh On Daf Mem (40) states that Shimon gets 3 portions, 2 from Reuvain who is the Bechor and one from his own portion.