Sorry you are here brother. I don't have much time right now but i just wanted to jot down a few quick notes.
Detachment is not the same thing as not talking to your W. Detachment is emotional in nature. It doesn't mean being cold, cruel or distant. Its about not letting someone elses behavior affect your emotional state.
You mentioned what your W "should" be doing. You need to drop that word from your vocabulary because it means that you are not detached and you are not putting your focus on YOU which is where it needs to be right now. You need to be completely unconcerned with what she "should" be doing.
Do not contact your W to ask how the kids are doing. The only reason to contact her (and really, you should be waiting for her to contact YOU unless it is an absolute necessity) is if it is an emergency or you need to discuss some last minute kid schedule stuff. But Ideally, you are waiting for her to contact you. I know you want to know how your kids are doing but you can find out when you see them next and it sounds like you see them all the time. Get on a schedule with them as quickly as you can and try to stick with it. I had a schedule with my W but I wasn't too strict with it if varying from it meant that it was good for the kids. My kids stayed with me when I kicked my W out of the house. I take them to school every day and my W picks them up every day. 2 days a week, she was supposed to take them to her house for the afternoon/evening but I didn't care if they wanted to go a 3rd day. I didn't care if the kids wanted to stay the night at her house on "my" weekend. So long as I didn't feel my W was taking advantage and it was the kids wanting to alter the schedule a little, I didn't have a problem. Put your kids first. Become a killer dad. Be ridiculously awesome. But don't be a doormat either. Adopt the persona of a gentle giant. Talk softly but carry a big stick. Be tender in all your interactions (even W your wife). You don't have to be mean to be detached.
As for this weekend of hers, take the kids. Plan something awesome. Send them back to her with stories of the freaking fantastic time that you all had together (without her). Make those kids BEAM with joy. Show her what she missed. Dont worry about what she may or may not be doing.
Sorry, that ended up being more than just a few notes.
Me: 48 y/o W: 47 y/o Together: > 20 yrs BD: Dec '15, then S 2nd BD: Mar '16, then I filed for D April '16: started piecing