Thanks again everybody. There is a lot to think about here. The situation is complicated! I can't go into full details but will share the following:
-We live abroad, in a rural isolated place. DD is on PTA and tries to be involved with local mums, but locals here have very different lifestyle/family dynamic - its not as easy as UK for social mixing, and we are all a drive from any neighbours etc.
-DD is left very isolated, despite ongoing best efforts to mix, partly because she can only pop out briefly Mon-Fri because of kids routine, partly because all her w/e and hol time is reserved for SIL.
-When new baby was born last year, SIL chose to switch to a job with more travelling - he's now away from home Mon-Fri, 2 weeks out of 4.
-SIL is very much a weekend/holiday dad (and husband). Not at all involved in day to day family life or household business, even when home. When he's home they go out for meals, go for trips, have his friends come to stay from UK etc.
-We share day to day childcare with DD - school, medical appts, shopping etc, because if we didn't, she would be alone with it, and because as i said, we love them all and enjoy being togther.
-SIL earns very well. They are very well off.
We are not, and I do feel he takes advantage by not at least ensuring we have shopping and petrol and an occasional something as a thank you (having said that, DD paid for a big shop with me this week, but it was of course for them all, as staying here this week, and every other week).
-Situation further complicated by my DH himself being childless. He is happy to spend 24 hours a day with GC, whilst in all honesty I would prefer a little more time for me/us.
Ah well, it is a bit of a conundrum. I try to insist on time for me and DH, but am so tired from just having the GC around so much. DD does most of the work, but I find just playing with them, carrying them, picking up, putting down, clearing up after them etc, 5 days a week, very tiring. Often when they go all I have energy for is a big house clean and the business work, not for leisure pursuits hobbies or social life.
I wish SIL was a hands on dad, and a more involved caring partner to DD, or that DD was a tougher cookie and would tell him to get his finger out when he’s home! But neither is the case.
Our situation evolved when DD had first child, no help or support with childcare at all from SIL, home or not. We stepped in as she needed us.
We hoped by demonstrating loving childcare it would be good example for him and for her and would make him pull his bootstraps up, but he just used us, I think.
We tried to back out a bit when we realised that, but DD got pregnant again and lost baby after miscarriage - he was no support before or after. We had no choice but to help as she could not manage.
Then she had 2nd baby and again, he just abdicated responsibility. Again, we really felt we had no choice but to help.
And now its sort of custom, that we share childcare/help raise the GC, but with no financial or other overt recognition of that fact.
So yes, although I love DD and GC, and love spending lots and lots of time with them, I'm overstretched and not all that happy with the extent of arrangements and the lack of acknowledgment, financial or otherwise, of the level of our input.
There - now I'm sure I've said too much. Thank you for listening everyone!