DSis is married to BIL, nice enough guy and loves her to bits.
He has 3 DC - two mums (this is relevant).
His DC's names have a 'theme'. Think like the Kardashians, names spelt slightly unconventionally to go with a first initial which is also BIL's name and first initial.
So let's say he is Karl Kooper and his kids are Kolin, Khloe and Kathy. All have his surname.
Both his XPs happily accommodated his preferences and all DCs have his surname too.
DSis now expecting their first DC. She likes Olive for a girl and Ben for a boy. She did take BIL's surname.
BIL says baby won't 'go' or feel like part of the family (DSCs around a lot). He wants another K name. His suggestions are 'real' names like Kylie and Kevin.
DSis is wavering. I think she needs to take a stand! This is their DC not just his! Feels like an ego trip to me.
On the other hand, the DC will be part of a larger family. Maybe they would like to 'match'?
AIBU?