Yevamot 95: Returning from the Dead (with implications for your marriage)

A dispute between R. Yehudah and R. Yosei on a dispute between Beit Hillel and Beit Shammai over cases of a husband who believes his wife to be dead, and sleeps with either the mother-in-law or the sister-in-law, and how those scenarios would impact his marriage, in the event that the wife turns up alive, after all. Plus, the rationales for the approach to permit the couple to return to each other. Also, R. Yosei. On a case of two couples, where the wives are sisters, and the testimony on disappearance that is found to be mistaken. What are the implications for the couples to be able to return to each other? And who is disqualified from being with whom? Note how complicated and ambiguous the mishnah that this Gemara works off of to interpret is.