My DS1 has a really good relationship with his grandma. If I let him, he's probably go and live with her and my dad! He visits 2x a week and sleepsover one night. What gets my goat is that I feel my mum is trying to undermine me and get my DS1 to love her more than he does me. She's always been critical of the way I've parented him and had a real go at me recently for being too hard on him over an episode of bad behaviour. I could go on but basically, if I tell DS1 that he can't do something in my mum's presence, he will immediately go to his grandma and get what he wants (the thing that I said no to).
He's allowed to eat what he wants at her house (chocolate for breakfast), watch as much TV as he likes, he only has to say that he wants something (eg a toy) and my mum will be there promising to get him it.
Aaargh.
In the end, they are very good grandparents to DS1 despite all the spoiling, it just gets to me that I always, always look like the bad guy while my mum is the all-giving lovely person who always say yes. DS1 is always saying to me "can we go to grandma's?" and when i say, no, not tonight, he acts like being at home with me and DP is the most horrible thing ever!