Help with actors and actresses?

Okay, so for my seventh grade english project we have to find actors and actresses to play the characters in the book roles'. The book is Countdown by Ben Mikaelson. We have to describe a boy named Vincent who is an African Maasai, 14 years old, He is interested in learning and fights a lot with Elliot. Elliot is also a fourteen year old boy from Montana, and is the first junior astronaut. They contact each other on radio in space, and he is very head-strong and determined. He will do whatever it takes to get his way. Then there is Mandy. She is a girl who was Elliot's alternate in case he did not p the requirements to go into space. At first Elliot and Mandy had a rough, ,and competitive start but became the best of friends in the process of training. When Elliot is in space he misses her deeply. She is kind, very intelligent etc. He develops a crush on her. If you were to see this book in a movie what actors would you use, to play them?