Sorry you are here .. even more so on this side of the forum and yeah .. its not easy nor is this road quick.
Read up a bit on your sitch .. not entirley but some of the back story.
Seems your W will need to deal with that abuse, thats when started this avalanche ... seen Heavy asked about death/ trigger .... I think that in your case her divorcing her parents was not the trigger ... read up on MLC and you will see they start breaking contact with anyone and everyone close ... strange thing with your W is she knows about the abuse, maybe she has become so angry about it .. has not dealt with it that it started this thing off ... at any rate its all a guess.
So some survival tips for MLC that I learned .. took longer than I had hope to learn all this .. but again .. part of MY journey:
Pressure is bad .. any kind .. pressure about OM, pressure about the D, the house ... even pressure about selecting a color for a wall ... anything will get em spinning.
Like you mentioned .. long game here .. that part suck$, not talking weeks or months, but with that ... you have control of when YOU are done here, because there is no guarantee they come out of it, its possible but holding on to that will drive you crazy.
Bottom line .. and this is where the DB is a life saver, you have to focus on you and your kids at this point. You can not fix her, this was a broken spring just waiting to break all along .. finally it was wound so tight it snapped. Alot of what she has said ... the mean stuff .. yup .. it happens .. it hurts but seems they have to channel the hurt and frustration and guess who is the lucky winner of that honor ... yup .. you.
As far as OM, let it go .. that will run its course, she will realize he is not helping ease her pain after a bit .. or dude will figure out the crazy is not worth the amount of energy required .... mine broke up with hers atleast 6 times or vice versa.
So you can expect to see her act as a Teen who has a fake ID during spring break for a bit, its par for the course .. during this time, start living your life, make the changes in yourself you want/need to make ... you will have to reinvent yourself regardless at this point right? Might as well start now.