Don't take this as anything but well meant, but you will only ever be treated as you will let others treat you!
I made sure from day dot with my family, that they knew I had had a rough start to life until I hit my twenties, I was everyones doormat, I was miserable, put-upon, felt unloved and unworthy as family just saw me as someone to dump on, so, I told them (smiling and with lots of cuddles!) that for the rest of my life I would dedicate myself to making them happy and loved, but only if they promised to do the same with me! :-)
Happily, they understand that if people treat me well, help me out, love me lots & don't expect me to do everything and are grateful then they get sweet lovely Mags, however, anyone takes the mickey, or shows one inch of being ungrateful for the things I do, then it stops. No ifs, no buts, we are a family, we work together or I'm on strike!
I hope you have the strength to fight back a bit and enjoy your grandchildren, you'd be lost without them. x