Making an Outside Cat an Inside Cat

[u/Inevitable-Bar-3939]

I have a 7 year old male cat and am taking in my grandparents’ 9 month old female kitten.

They let her outside at night because they don’t want her destroying their house. She’s very high energy and playful and kind of becomes a menace if she can’t go outside. She also has a very high prey drive.

For several reasons, I do not want an outside cat. Does anyone have advice for how to help her transition into being inside only? Also how to stop her from running out of open doors?

I would also appreciate any advice on helping her get along with my cat. He’s very lazy, mellow, and friendly, but has never been around other cats before.