Starsky, you had mentioned in my other thread about the safety of the kids.
While it concerns me greatly about the amount of time she leaves the kids alone on weekends, even over nights 'til... ? I don't know. Until she gets home the next morning...? I do trust that they will be physically OK. I am right here and always available if something were to go wrong. Both know how to get in touch with me if there was a real, safety problem.
But emotionally...??? They will both be scarred from this. How severely, I don't know at this time. I will simply have to be the best dad I can.
So start.
Enforce this boundary. "Wife, if the kids are going to be alone with no adult in the house past 'X'pm (I'd suggest 11pm), I expect for you to either arrange for an adult babysitter or let me know so that I can come and sit with them until you're home. If you feel the need to stay out until 3am -- or later -- than it would probably be best for all concerned for that to be a night where they stay with me."
You've said yourself there's no 'mistakes' to make here, and nothing to 'try' anymore . . . why are you so reluctant to enforce what you KNOW to be the right thing for your kids, Kaffe?