I understand that you believe his dad should be involved in the C sessions. I certainly agree with you.
However, trying to force things your way is not always the best way to help them go your way. In the case of STBX's involvement with C, he will likely get MORE out of it the MORE you back off.
Each time you butt in and try to manipulate/control/influence/coerce/encourage/manage (choose your favorite word) HIS choices, you make the C about YOU rather than who and what it should be about — him and his R with the kids.
Great he has the appointment! :-) Now, leave him alone.
Get your focus off STBX, HIS life, and HIS choices. Here is a question for YOU: Did you give STBX a chance to succeed and make good choices on his own in the M or were you always fixing/pre-fixing-even-before-there-was-a-problem/managing/anticipating/engineering/"helping"? If not, giving people space to shine and grow is a good skill to work on now and this whole thing gives you a great opportunity to do so. You gotta work your issues out sometime, may as well start now.
