"I don't know how to ask people to only buy for my son and not for me."
I've been trying to stop the buying between Adults in my Family for years.
This year my middle DD is skint, so between us, we put to the others that we wasn't buying presents.
My Sister (the main one who gives us shit, whilst she gets a £100 combined present), kicked up a fuss. My DD said "if you don't want to buy for the kids, fine, they'll be happy just meeting up" and we've stuck to it.
I'm giving my children money, but that's my descion, I don't want anything back.
When I was with my ex, I refused to get into gift buying for his Family. I was a LP and my children wasn't going to go without whilst I bought for others. I made it clear, early on in the year.
I value time spent together. I'd rather people put in the effort to do a Christmas Market and have a winter cocktail etc.