Hmmm Im in same situation I guess. Im an only child, whereas DF has brother & sister both with 2 kids each. Ummm his family calls me 'Aunty Lissy' to the kids so Ive just run with that, but I would also be ok if they didn't. I guess I dont really have an answer for you coz Ive just gone with whatever his family has felt comfortable with. As for how I feel, I spose I feel closer/'Aunty like' to his oldest nephew, who was born well & truly before I was on the picture, but we have seen him the most & he has been to stay with us. Sounds horrible but I feel so much closer to some of my friends kids than I DF's neice's & nephews really.