I know that this isn't easy. At least you have this place which means not only do you have great support,advice and friends but you also have another invaluable advantage. You know what you are facing from other stories. You also know there is nothing you can do to change the situation now. All you can do is the best you can in that situation.
I hope too that you realise that you are better off without her in your life. She has no respect nor consideration for you or others. At the moment she is not capable of doing so. Maybe down the line she will but for now she is off team gordie. Part of what we learn through our situations is the stand up for ourselves and how we let others treat us. We do this mostly through boundaries.
Whereas I am not for D nor separation, I think that you are right to be pushing forward now. You have been patient over the last five years but now she has crossed a line. I personally would want her out of the house asap. But as others have said, you need to be firm but kind. Revenge, anger and other negative feelings should be kept out of your interactions as much as possible. This isn't about not upsetting her etc but moreso about you rise above the crapp situation she has put you in. I have seen men around me be consumed by jealousy, anger and whereas I understand it, it truly isn't a good way to live.
I feel for you with all those kids. It won't be easy. Only you can decide when to tell them. They need to he protected and supported and definitely not as weapons against each other. That being said, your W will have to face up to her choices once they know. I doubt that will change her mind, but will add a layer of reality and complications to her new life.
I know that this isn't what you wanted, but it's what you've got. Accept that and make the best of it. I too had a W free weekend and I liked it. Me and my boys. It was good. My W wasn't away with OM so that isn't comparable but her absence lifted a certain level of stress and poor interactions. It'll be sad in one way, but liberating in another when W does go. Look forward to that.
Got to go. Take care
R 25 years M 14 years S11 & S13 Working on it alone since Oct 2014 M in trouble a lot earlier (~2 years) Feb 2016. 1st R chat in a yr. Next R chat Aug'17 Still together