Wasn't his mother's village destroyed or something like that? Or am I mixing it up with something else?
I think he wasn't told of his clan to protect him against anyone who would have tried to kidnap the Fourth Hokage's son. Also the village despised him because he had the Kyuubi sealed inside him and instead of blaming the fox alone, they decided to project the blame on the boy carrying the demon inside him -_- What can you say? People can be very stupid.
As for the relatives ... Who knows? Maybe Minato was only child. I haven't read up till the last page so maybe they mentioned others, but so far they didn't say anything about Minato's family.
Mind you, I base my answer on the chapters which I have already read and that's till volume 54. When I get more time, I'm going to read the rest online, so it could be that my answer above is wrong ^^;
Sorry if that's the case, but this is just what I think based on what I can remember from reading