Your posts make me so sad. You and your sister are choosing to bury your heads in the sand while your spouses carry on an affair with eachother and you all act like a happy family. It is so sad. You are both experiencing some awful denial.
I may have told you this story, but a close family member of mine is having an A. Her H doesn't know, and she said to me "If my H found out, he probably still wouldn't leave me or be a man about it, and he would turn his head the other way. I can't tell you how much of a turn-off that is, he has no balls" She has told him she is unattracted to him and staying with him for the kid and there will be no sex. And the fact that he is willing to live with that turns her off even MORE.
This is what you are currently doing by pretending. You think a weekend trip with your kids will bring her back from an A? No, she will probably realize how nice it is to have a weekend alone. Please, us mother's love that.
Your toleration of her disgusting and disrespectful actions I can just about guarantee are very unattractive in her eyes.
And how is this benefitting you in any way, playing happy family while she is having an affair WITH A FAMILY MEMBER?!
You can bury your head in the sand hoping by some miracle she will just decide she wants to be committed and treat you with love and respect (highly unlikely) or you can continue to bury your head in the sand and understand your present situation will not change if keep going as you are, or, you can begin to respect yourself and not tolerate what your wife is doing,
The choice is yours. At this point, the outcome is dependent on your decisions, not hers.