I'm going to kick my friends/roommates sister off our hulu account
Why are you going to kick your friend's sister off the account?
Yes she always buys movies in my name when she watches them
It sounds like you are justified kicking her off the account. It is rude to continually buy movies with other people's accounts.
I think so. I will take care of it today.
I think that you are doing the right thing. Your friends can learn some responsibility too.