Rain will act, or at least try to act, like the mature one. Already he's...eh...trained with a sword. I don't know about her. but his sister will probably be the headstrong one. She be the first to act, and might get a hold of something new a bit faster then Rain.
She and Rain will be quite different. I don't just mean by normal standards: Rain wil be able to do things she will only dream about. It comes with being in my bloodline. She is the daughter of two Wonderbolts, and one of those is the fastest one in the world *gestures to you*. Rain may not be as fast, but he will be a lot stronger, and more resilient. It will be a contest between the two as they grow up.