Why does the Torah see fit to tell us that Amram married Yocheved, and Aharon, Elisheva bas Aminadav (in Pasuk 23)?
Ramban #1 (in Pasuk 23): It mentions the name of the mother of the prophets (Moshe and Aharon) in their honor, 1 and the mother of the kings, to teach us that she was a Meyucheses, from the family of kings, the sister of the celebrated Nachshon.
Seforno: To teach us why he merited to father the leaders of the generation from whom the Kohanim would ultimately be chosen. 2
Targum Yonasan: Refer to 6:16:2:4.
Baba Basra, 109b: One should always marry the daughter of 'a good person'
Ramban: And to teach us that she was the daughter of Levi the Tzadik, hinting that a miracle was performed with her - that she bore children at the age of a hundred and thirty.
Refer to 6:23:1:1. Seforno: And it is for the same reason that the Torah tells us that Elazar married a daughter of Putiel, who was a leader of his generation. (Presumably, it is for the same reason that the Torah tells us that Amaram married Yocheved - though it is unclear as to why the Seforno fails to mention it)
Whilst he was still a priest to Avodah Zarah.
How could Amram marry his aunt, since relations with one's aunt is Chayav Kareis ?