Hmm difficult one. We tend to treat our daughters and family to meals out as we are in a financially better position as they have mortgages, childcare etc and we are now mortgage free and although retired we still have a good income and savings. They usually offer to cover their food though and they do treat us occasionally. They are also good with money and don't chuck it around as far as I can see. They have high mortgages though, are paying back student loans and have childcare bills for our grandchildren and I remember how tight money was for us when we were at that stage in life. My mum also generally treats us even though we can well enough afford to pay but she says she likes to and we live a long way away from each other. We also do insist on treating her sometimes and always remember birthdays/Christmas gifts and cards etc.
I think you need to have a discussion with your DS going forward maybe when you arrange your next get together. Do you feel uncomfortable saying you cannot afford to pick up the whole bill and give them the option of choosing somewhere cheaper? I strongly suspect the meetings may be less frequent if you are no longer paying so would you be ok with that? No way should you be pushed into remortgaging.
Reform - Disgusting Misogyny - and more!
Cheap and Easy to Tend seasonal plants for my garden tubs

what a horrible thing for your d.i.l. to say. Was your son there and if so what did he say?
.