- you can't control your sister just like you can't control your wife. If your sister wants to spend time with the kids and your wife, that's ip to her.
- she's still your wife. She's still the mother of your children. If you can't trust the kids to be taken care of on her days, who can you trust?
- as for your vacation, do what you want to do, but do it for YOU. Now, if your accounts are joint and a trip stresses it, I would be wary. If you do get to D proceedings, flagrant spending could come up and it may not be looked on favorably. I'm not a lawyer, so I'm not going to pretend to give advice. But I wouldn't spend beyond your means right now.
