You are right, I don't know your sitch, but anger is your enemy in cases like this.
Things seem fast to you, but your W told you she was done a year and a half ago, and was probably done 6 months before that. For her, she has probably been emotionally divorced for two years, while you don't yet feel emotionally divorced. It is a very difficult place to be in, and I feel for you.
But relatively speaking, STBX sounds OK from your post. Lots of WASs buy a house with the OP within days or weeks after moving out or move in directly with OP, your STBX waited much longer. She also seems to have taken time introducing kids to OP. From here, she doesn't really look out of control. The older kids can help with younger kids. Blending families is hard though in any case. But for the sake of your kids, I hope the new family works well. Your kids have two families now. Let us hope both are loving and safe places.
Of biggest concern is that you are learning this stuff from your kids. That puts them in the middle and isn't good for any of them. If you can detach and let go of your anger, perhaps there can be improved communication between you and STBX.
Don't try to control her R with the kids or his R. Wish them well. Intervene only for REAL legally enforceable concerns about safety. OP is already in the step-parent role, not much is going to change that. The best thing you can do is to accept this and genuinely wish them well. More than anything, your kids need to be able to feel safe and loved in both their families without feeling like they are betraying the other parent. Only you can give that to them.
Perhaps you can email STBXW:
"Hi STBXW,
Apologies if I've been hard to communicate with. I hope we can communicate about significant life events that affect our children through email for their sake. In recent months, I've learned through our daughters of your job change, your partner, and your new house. This puts them in the awkward position of being the bearers of such news. I think it would be better for them if I learned such things directly so I'm not taken off-guard. Shall we try to improve communication for the kids?
