Bertrand - So your partner’s mother and your children’s grandmother is not “immediate family”?
Err, no. By immediate family I mean my DH and my kids.
My inlaws are lovely people, get on with them fine, but we don't live close and I wouldn't include them in any celebration for me, we are very different (they church going, very straightlaced, teetotal - nothing wrong with that but different to my family) and also I am not into big get togethers, prefer just my own little family. Hence not particularly wanting a big silver wedding. Would prefer to spend the money travelling!
I have no problem with being involved with inlaws at Christmas, when its DH birthday, or one of their celebrations, or the kids (they were invited over for DS 18th and will also be for DDs next year. Unfortunately my mum was too ill at DS's to come over and died shortly afterwards). But not for my own birthdays. And TBH they wouldnt expect it.
As for my mum, my relationship with her and brother was very difficult, he was golden child, never did anything wrong, she was jealous on his behalf that we had a comfortable lifestyle from working hard, he had nothing as he chose never to work. She always made snide remarks about me, I was always in the wrong.
Why would I choose to spoil my special birthday celebrations by inviting her, and yes it would have spoilt it. I spent many Christmas days and holidays (we sometimes took her to see Dads family abroad) in tears. Calling me fat (size 10) and many other names. Couldn't bring myself to go NC, she was a lovely grandma to my kids, but now she is not with us, DB and I are virtually NC after many years of him treating us all atrociously and it is bliss. I obviously never invited him to anything.