I think the problem is that we haven't been given enough information here. There are two potential scenarios at the moment, which is why I think you're getting such mixed responses, OP.
- That OP is being unreasonable and is actively damaging her relationship with her children and grandchildren
- That OP is trying her hardest to follow her children's rules around parenting, but the rules are actually too severe and she is constantly under attack/being criticised despite trying her hardest.
In the first scenario, the 'rules' might be perfectly fair ones, and OP's children might have communicated them in a very respectful way to her. For example, 'please make sure they do their homework before they can go out to play', or 'it would be great if x child has a nap at 2, otherwise he gets a bit cranky and overexcited'. These aren't unreasonable asks or rules. Furthermore, there is an element of having to accept specific parenting rules which you don't agree with, out of respect to your children. For example, I see lots of people saying that OP's daughter is being 'ridiculous' for not wanting her kids to roughhouse. I personally think that this is besides the point - she doesn't want her kids to roughhouse, OP should respect that and tell her husband, 'no roughhousing'. It's not a matter of her kids not 'trusting' OP, it's a matter of her kids being parents and by nature having a slightly different parenting style. Likewise, when I have kids I will ask my much-loved mum to not put academic pressure on them. She's a wonderful mum and raised me and my sister excellently, but one thing she did do which wasn't great was pressurise us a lot about academia. I've already spoken to her about not putting academic pressure on my kids, and she has agreed to out of respect to me, although she doesn't agree with it. By dismissing her child's concerns about roughhousing as 'ridiculous', OP is effectively undermining her children's parenting.
In this context, OP blocking her child for (politely) asking her to not encourage roughhousing is petty, and risks damaging her relationship with her children and grandchildren. I know that I personally wouldn't feel comfortable having my child looked after by someone who acted like that after I tried to lay down a reasonable boundary with them. It suggests an inability to listen and an unwillingness to look after the children in a way that OP's daughter deems to be safe and healthy.
In the second scenario, OP's children communicate with her abusively and aggressively, effectively demanding childcare while also endlessly criticising her. The criticism is nasty and petty ('why did you do x child's hair that way, the hairstyle looks ridiculous', or 'x child is not allowed to get her coat dirty when you go to the park together'). Furthermore, the criticism is unjustified - OP is an excellent grandparent and tries to provide her grandchildren with a stable environment in which to work and play. She feels the need to ask her children permission to do even basic things with her grandchildren, such as taking them to the park, because she feels so much scrutiny.
In this context OP, it would make sense for you to lay down some boundaries as a grandparent. For example, 'I'm happy for you to share feedback, but you have to be polite and respectful', or even, 'I don't feel comfortable or safe looking after your children at the moment because I don't feel that the rules you have set are ones I am able to follow, because they are too rigid. I'd love to see my grandchildren, but maybe we could all go out to lunch together instead. This would mean that you are able to parent your children to a standard you are comfortable with, and I get to see my grandkids. How does that sound?'