my brothers kids are our nieces and nephews - they call DH Uncle Boof, and have done pretty much the whole time we've been together.

DH has two siblings from whom he is estranged, and they both have children older than me (DH was an oopsie for his parents) - even though i have a minimal amount to do with one of his nephews (out of necessity) i do not consider him MY nephew - he is simply S, who i am forced to deal with. i think if the relationship status was different my feeling would be different. the estrangement also means that if we are ever unfortunate enough to run into DH's siblings again (one lives less than half a km from us, but doesn't know we're here) - at the shops or something, and they try and play the "aunty" card, they will be told in no uncertain terms it wont' be tolerated

we do have a lot of other "surrogate" Aunts and Uncles in DD's life though! she isn't missing out!