DP and I both work full time so rely on both sets of grandparents to help look after our two DSs (8 and 4) after school and in holidays.
My MIL is a real pushover and let's the boys get away with murder. Sometimes this can be problematic but I put it down to grandmother's prerogative.
My mum, on the other hand, is the opposite. I wouldn't mind if she were just strict, like my dad, but she's often just mean and bullying. If one of the boys gets upset she'll mimic them and call them crybaby. She gets cross at the slightest thing and just yells at them. Her blood pressure is through the roof because she gets so angry all the time. She won't spend any time "doing things" with them and expects them to play quietly all the time.
My in-laws are away for the next month so my mum will be having the kids more often and this fills me with dread. She had them all day on Monday and reported that they'd been awful and rude to her. So today I sent them to her with puzzles, books, DVDs, arts and craft stuff and tickets to the local soft play. I also got the boys to help draw up some rules about behaviour and explained they'd only get gaming time at the weekend if I got a good report rom nana.
Apparently they were really good whilst my dad was there but when he went out it all went downhill. He came home and my mum had got a stick from the garden "just to threaten them with"!! When I questioned ds1 he said they'd been watching cartoons happily but nana changed the tv so she could watch neighbours. I'm not really surprised they played up. 
I know my kids aren't angels and can be hard work but I'm so cross that she treats them like this. She's 73 and won't be here forever and I'd like my boys to have fond memories of her. As it is, they refuse to kiss or cuddle her and tell me that they hate going to hers.
I've recently attended some voluntary parenting classes at the school, mainly to get some pointers over sibling rivalry, and it's really made me think about better ways to communicate with my children e.g. Using positive encouragement, giving them choices and consequences, being more nurturing and less critical. I've tried to share these techniques with my mum but she just smirks and rolls her eyes. She thinks naughty steps and reward charts are nonsense.
She was like this when I was a child (I distinctly remember her being too busy watching Knotts Landing to hear about my first day at high school!) but she seems worse as she gets older.
I guess the solution is to get a childminder or some other arrangement but I wonder if anybody has any suggestions on how to get her to, I don't know...."like" her grandsons more. 