If your lover is keeping you away from his or her family then chances of his/her sincerity are very slim, because if s/he is part of a family, not like me, living away from them without any strings attached, so they will never effect my relationships unless the person gets scared of them 😉 which will be wise! But, had I been living with my family members, they might have influenced my relationships, if not in the beginning then possibly later, you know, blood relationships mostly are quite strong, and so is their influence.
Ask poor in laws of both side who had ended up with a bad fish, not all cases are bad, often they just fit in, but often the in-laws regret that “had they known….”
So honestly, if your lover does not invited you to his/her sister’s marriage or brother’s marriage you can smell rats
Anyway, any lover who truly loves his/her lover will prefer having him or her around when s/he is having fun, right?