I'm another one with a MIL who pretends to the world she is a doting grandparent, but in reality doesn't give a shit. She sends a birthday card if she remembers, but that's it, no present, no call. It's not about material things, as tbh, she could buy them a box of maltesers or something and they'd be delighted, it's the fact that she tells everyone what a tragedy it is that she lives too far away to see them more frequently, but never calls to ask how they are, or to talk to them, or spend time with them when she comes over. We are never invited over, and she lives in a pigsty with an abusive husband, so we'd never stay there, but there are loads of ways she could be included and she just cba.
My mum rings at least once a week to chat to them, sends them letters and cards and knows about all the important things happening in their lives. They're not well off either, but they buy small, meaningful presents that they know the kids will love, because they've bothered to spend time with them and know what they are into. I have no childcare expectations from them, but they come and stay monthly (also live quite far from us) and will always volunteer to babysit when they're here so we can go out. If I need them I know they'd be there.
Both the kids and my parents get tons out of being involved in each others' lives. My kids love them and will always want to spend time with them when they're older. You reap what you sow.
It makes me sad for the kids that they miss out on a relationship with the grandma, and also step grandma and aunties on DH's side because of a family falling out. But my kids are lucky with my family. I have 2 sisters who dote on them and they have lovely cousins. They will be fine.