Not my kid, not my responsibility. But then this moron stayed with this woman so...
‘He doesn’t know what to do.’
That settles it. Make him the dad. Heh heh.
Treat the kid well. As part of the family but have the wife sigh paperwork that she forfeits all claims to him and his (kids, family, money) in the event of divorce. If she is “willing to try again” then this judicial revocation of rights should be a no issues. Nope, the file for divorce with prejudice. Ask for his kids and she can get Child support from the donor. Risk nothing win nothing.
Wait until the kids old enough to want to be adopted.