I am an only child and I have an only child so I am unsure if this is normal. DH doesn't have a great relationship with his mother, mainly because he has always felt that she massively favours his younger brother. She subs his wages, takes him on holiday, generally sorts out his finances as he has got himself into dire straits in the past. It isn't even just about money - he is clearly the favourite based on the amount of time and help she gives him.
Anyway, DD went out for lunch with her the other week and MIL actually said to DD that she is proud of DD, she is proud of DH but she is extra proud of BIL because he is dyslexic so he faced difficulties in school. I just can't fathom thinking and saying that. But maybe everyone with more than one child feels that way? Maybe it is usual to be more proud of one child than another?
For context, DH is extremely independent, we don't ask MIL for anything. She knows we have very different political and social viewpoints to her so conversation is superficial. I just feel so sorry for DH that he has worked so hard but it will never be hard enough for her.