Yes, I didn't tell the whole boring story - we discussed doing some things as a family, and some things independently, and I have spent zero time as a family with FIL. Frankly, I don't enjoy spending time with FIL - he yells and doesn't listen - big surprise - but I am holding family time as sacred for S. It was just a discussion on which day was family day. I was not inviting myself per se.
My question about tonight also lay in that tonight is my night with S. (H has S yesterday and today) so it was clear that I wanted to be there with S.