It's a matter of personal choice honestly.

People RPing as Hermione aren't really going to get a lot of votes from the SS crowd. Firstly it's impossible if she's a firstie and secondly why? Why are you being so uncreative as to have to resort to someone who's already been made up?

RPing as distant relatives should be allowed. People have built family networks on SS and have fun saying this is my cousin and really meaning it. I think people who want to play canon characters should have a good idea of what their characters parents, age, home ect are. Or you'll just confuse yourself.

People like Cassirin and other members have thoroughly researched their parts. They RP knowing full well who their charrie is. And when you talk to them it's obvious they know who they are.

If your clear and the rest of SS is happy then why not? Nobody seems to care if you great uncle is James Potter II just don't try and get Hermione to be your mum.