My son has been in several different types of rehabs. None of them actually had family meetings! We did enjoy seeing him and kept the conversation positive. I know this is hard for you as I believe your son wasn't that excited about starting the program. I would keep the visit light and not probe too much with him if he doesn't want to share. Remember its a process and recovery takes time. Enjoy the ability to see your son sober and give him encouragement that he is doing the right thing.
Hugs
TT