@redleg cvs! Yaakov a bonus, bichir haavos, did not do something wrong!! There are answers how it goes with the lav against marrying two sisters but he did something right, not wrong.
Another answer is that mitzvos were optional Hiddurim which the avos of course kept unless they conflicted with sheva mitzvos bnei noach which was incumbent on them at the time. Of course this changed with matan Torah.
He married them because he otherwise would have broken 1 of the 7. I remember it being that he had promised Rachel he would Mary her although can’t remember how that was one i of the seven right now…. Unless I’m mixing things up.
Actually I think it was that it is mutar for a Ben noach to marry two sisters from different mothers, and since he had promised to marry Rachel, he couldn’t break his word for the sake of a chumra