I know exactly what you mean.
We had the same with IL's. In fact, a couple of years ago I could have written your post
What happened was that my kids b'days are at Xmas. So IL's bought them huge b'day presents & then even huger xmas presents. We used to be affronted when some of the stuff they bought for b'day had been what we had got for their Santa gifts.
It all came to a head 2 Xmas's ago. They came up on Xmas morning with a black bin liner full of gifts. 3 of the things MIL bought for dd were the same as she had gotten from Santa, and to make matters worse, MIL knew I had bought them for Santa. Anyway, I had words with her & she went home calling us ungrateful.
We didn't speak for a few months, way into last May, actually it was for FIL's b'day that we spoke and that is in May.
Anyway, they had a huge bust up & the fall out affected everyone badly as Dh worked with his dad.
Long story short, I went down on my own one day, had a drink with MIL, we both talked, dh called after work, we made up.
They just didn't understand the money thing, they said they had money & just my 2 kids to spend it on, please would we let them. We just said that my parents weren't loaded & had 17 grandkids... made them see it that way. Let them know they didn't have to buy the kids love... they have now realised that my kids adore them, & they never ever expect presents from them. Every now & then they will give them small things, like colour pens & a t-shirt etc... but I can live with that
I sincerely hope you get it sorted out, as I almost lost the kids their grandparents by my silliness
Good Luck xxx