Do you say 'My nephew/ niece' or 'Our nephew/niece'?

I know that technically it is 'our' nephew but I say 'my nephew' because my nephew is from my side of the family.

If my brother-in-law had a son, I would probably say that it's his nephew.

It's only really for distinction purposes. So other people know to look at me or him to figure out which side had the baby. (My brother and SIL just had their second son. Yay! I'm a happy aunt.)