Amram is listed as one of the four people who never sinned Shabbos 55b along with Binyamin, Kilav and Yishai

Amram married his aunt Yocheved (Ex 6:20) which is prohibited by Vayikra 18:12

Moreover Amram divorced Yocheved after Paroh's decree and only agreed to remarry her after Miriam rebuked him; however Yocheved had been married to another man in the interim TARGUM YONASAN 11:26 which is prohibited by Devarim 24:4

Let's answer this problem with everything that Rabbi Kornfeld writes in the name of the commentaries on http://dafyomi.shemayisrael.co.il/parsha/vayigas3.htm

to defend Yaakov, Amram, etc. (Ramban, Maharal, Chizkuni, Ohr ha'Chayim etc.)

The question is according to many of the commentaries it seems like pre-Matan Torah there should have been many more people to never sin. Specifically, using the the Ramban and Maharal approaches for hundreds of thousands of Jews pre-Mattan Torah in Egypt. How could they sink to the 49th level of Tumah? They were transgressing Sheva Mitzvos B'nei Noach, everyone accept Binyamin and Amram.

Even more difficult is how could Binyamin and Amram pre Mattan Torah be on the same list as Yishai and Kilav post Mattan Torah - if the criteria is drastically different how could they be grouped together. Seems like Yishai and Kilav are on a higher plane than Binyamin and Amram

Is there a way to understand the Gemara on Shabbos 55b differently that makes sense of all this??