I do get where you're coming from op and I think this situation will only get worse. The best thing you can do now will be to find alternative childcare IMO.
My parents (mum mainly) looking after my dc has caused huge bad feeling in my family and seriously damaged my relationship (and the dc's) with my parents.
When I was preparing to go back to work when ds1 was approaching 10 months, my mum assumed she'd be looking after him (3 days a week). I tentatively brought up the 'are you sure' conversation and she was almost affronted and assured me of course she was.
I was happy - happy for ds1 to spend time with grandparents rather than in childcare and happy to save a huge expense - my parents are well off and wouldn't hear of accepting money.
All was well - my mum overstepped the mark a few times (feeding ds1 differently to his routine etc) but they were relatively minor and I learned to pick my battles.
Anyway, then ds2 came along. I was on maternity leave from the time ds1 was 2.3-3.5 (until ds2 was 14 months) so there was no regular childcare in this time, just the odd day of usual grandparents helping out stuff.
Ds1 was in part time nursery by the time I went back which was a pita. I needed childcare not only for ds2 but that would include nursery pick up for ds1. I mentioned this to my mum and got a resolute 'well of course your dad will pick him up' (my mum doesn't drive). Again, I checked and said we could think about a cm but my mum was adamant that they would do it. She's not one for big declarations so I never expected any 'my g kids are so amazing, I relish it' but she seemed happy with the arrangement.
So this went on for a year and a half, until ds 2 was approaching 3.
I then started getting the same as you op - sly digs from my sister about dumping my kids, no regards for parents etc. Then when I called my sister on it, it turned into an arguement in which my mum got involved.
Turned out, apparently she was hugely struggling and resentful of me leaving the kids with her 3 days a week. She'd been appalled when we'd had ds2 because she 'knew she'd end up looking after him too'. I wasn't grateful, never appreciated all they did for me in helping prevent the alternative situation where I'd be 'dumping my kids with strangers'. And of course, she'd carry on doing it to prevent that awful situation but I'd 'better not have any more'.
By this point she'd been looking after ds1 for 5 years (well 3 really if you take away the two maternity leaves). I felt sick to my stomach that I'd left my dc with someone - grandparents or not - that was apparently caring for them whilst full of resentment and feeling put upon. Hating every second basically but 'saving' them from the awful alternative of structured childcare.
I've lost all trust in my mum. The day we had that arguement was the last day she ever looked after them and we now have a cm. We've had several arguements since about how I've taken the dc from her and would rather dump (always that word) the dc with a stranger. I can't win either way.
I would advise anyone never ever to consider leaving their dc with family as childcare - the odd day of babysitting but never a regular arrangement. If it goes tits up there's no going back.