my mom was a PIA...had no respect for what others might wish, want or need - she already had decided those things and it was her way or the highway.
she was also a drunk. well hell, my whole family were drunks.
when renee was a toddler, she would complain about never getting time with her, so i'd have her babysit for a night out, whatever, and then she'd bitch about how exhausting it was keeping up with her.
when my daughter was in grade school, my mother showed up one day in her trans-van, took her out of school and took her down to the beach for a picnic.
i was mortified.
but.......
if you ask my daughter, who is 31 now? that was one of the best days of her life when grammy came and took her for a picnic at seahurst park.
my point is...don't forget which i tended to do, that while YOU see and react to your mom's actions in one way....a day trip to Lego Land with Gramma is probably the BOMB for the kids. no judgement on whether that is right or wrong...and no we shouldn't allow others to override our parenting - but spending time with a grandparent that LOVES you and wants to take you to do fun things isn't the end of world.
i never could get it right with my mom as a grandma. she died of liver disease when my daughter was 9. she really loved her grammy and has not one single negative memory. while she doesn't recall it clearly, when she was still in the high chair grammy would give her all the cherry tomatoes she wanted, and to this day Renee LOVES cherry tomatoes.
i feel for you. the balancing act. do what best preserves your sanity. it's ok to say NO to our parents once we are adults. but they don't often make that easy.