See if you can get her to agree with you at least before she talks to them. My W and I never really clearly agreed I am now realizing - she just avoided the subject but didn't neccessarily disagree.
The emotions may take over no matter what you to agree on up front.
I just mentioned today that she and I should have probably talked about it jointly with a counselor prior to sitting down with the kids. I don't think she would have been interested in that.
ME/XW:47 S21, D19, S15, S14 M:21 T:26 W moved 6/10 I filed 7/10 D final 4/12 remarried 8/12 W wants to R 12/10 and 4/11 but I decline