Thanks all. Ok, to clarify a bit....
They are 20 years old.
The first time I met her was last October, when they came here to dog sit, so we could attend a night out. When we got back from this night out, my son was sat upright on the sofa and she was lying with her head in his lap and feet up on the sofa. Me and DH sat with them for a bit with drinks before bed. DH sat in the chair. She didn't move, so I had to sit on the floor. I find that really odd that she wouldn't move (and a bit disrespectful). Anyway, after a few drinks, we left them to it and went to bed.
When we got up the next morning, they had left for the early train and we found take-away cartons all over the table, plus the plates, spoons etc. (I paid for this). They had wine, beer & cocktails, and the glasses were left all over the sitting room/on the floor etc. I personally, would not do that (at any age). I told my son off for the mess, but not her, obviously.
The next time we saw them, we went out for lunch. Not a special occasion. I picked up the tab (£135) and then when we went for drinks after, and we paid for every round. I wouldn't mind if we were loaded, but I am on almost minimum wage, so this is a lot of money for me.
I'm not going to say anything. When we got out this week, I will pay for everything. I suppose it would be nice if they bought one round, and yes, I suppose I feel a bit like this because I know that she is loaded.
I feel like the only time I can see them, is if I take them out. And that's hard as it's so costly. I've never been invited to the flat. I used to cook for my parents at that age, and I'd love it if they'd offer to do that.
Fwiw, me and my son have a great relationship, so it's not that there's anything wrong there, I think they just don't think. I guess that's the norm for their age though.
Aargh, I feel like a mean old husk now, for even starting this thread.