Purg, as hard as it seems, try to control your thoughts. Don't let your mind go crazy thinking about what they could have been doing. You know about OW already and you're still committed to saving your marriage, so whatever he may be doing is irrelevant right now. I know it's hard, but don't say anything to him. Just vent to us.
I know it is not going to be easy to leave your babies for 2 weeks, but they will be ok. Even if H will have OW do "the hard work", you know that they will be taken care of. You'll just have to remind yourself that.
Your H is getting nervous about being "alone" with the kids, so expect him to say things or act a certain way. Don't take it personally. Focus on yourself and remember to remain "zen". You can do it!
