I'm going to tell my sister to find a new place to live
Why do you want her to leave? Won't you miss her?
I'm going to miss her a lot, but I will find a hobby to contain myself from being bored
Family members don't always have to be forced to live with one another. Try helping her find a new place to live if you want them to leave. Or they may resent you for kicking them out with nowhere to go.
I'm a grown up now so I can do what I want.
That is true, you're the adult and you get to make the decisions if you own the house. Tell your sister you want to live by yourself and help her move out. Give her ample time to gather her things and be as accommodating as possible.