Make notes to keep yourself on track, try (I know it's very difficult) to leave the emotions out of it and just present the progress you've seen, any goals you would like to see addressed, and maybe a sort of aftercare plan for after therapy is discontinued. Make sure you, your son, and your husband are all on the same page before the session and if you feel like you're not being heard or validated, send your husband some kind of signal to take over.
It is hard to remove the "mom" in us when it comes to our kids. Ultimately, I believe parents who are truly invested in their kids know best. Stick to your guns about your plans - I can't tell you how many "experts" I've had to fight to try to find the right help for my son. Good Luck to you, sorry you have to deal with all this