Introduce new character in book?

[Rebecca Ambers]

I'm am writing a story, and there needs to be a new character. The main person is a girl, an she is 15, and he is 16, and no blood relation. Her dad has some family over, and he's there. (hes family friends with her visiting fam.) and at first they despise each other, but their parents are gonna make them get along. Her dads introducing them, when she comes home and he's there. How could this work? Thank you, and I promise I wont plagiarize.