Yeah, the ol' rollercoaster ride that many of us oldies are so familiar with. Strap in, grit ya teeth, and try and enjoy the ride (GAL, I mean). LOL
As for the agreement ---- do not back down or give in to anything, in my opinion. She left so she should live with the consequences as much as possible. Why should the kids, potentially, have to live 50/50 between two states/countries, and if she got them out of the country, who knows if she'll bring them back (I'm sure you've heard about that dad whose son was taken to Brazil by his mom, and now he's fighting to get back custody from the stepdad since that mom died). She's not the same person you knew. Maybe, that's why she's been so pleasant thus far --- softening you up so that you'll give in to wishes regarding the agreement.
Oh well! You continue being pleasant, but not backing down on anything, is my advice. She must face the consequences of her choice head on.
I think counselling would be a great idea for the children --- won't do them any harm and maybe it would do them a great service. One just doesn't know what's going on in their little heads. They may be thinking it's their fault mommy left, no matter how much you may tell them it's not, or some other stuff. Plus, it will strengthen any custody battle, if you are the parent seen being proactive in your children's wellbeing. (Although, I know you would be doing that out of love more than any other motive.)
Take care.
Me:57 H:52 M:28 Got another lawyer last year and filed. D35,S/D twins28,D22 EA4/04 End? Who knows? "Life is like a mirror. Smile at it and it smiles back at you." — Peace Pilgrim