Kenneth is a mutant. He is headstrong, slightly arrogant and very vocal. What should his powers be? His brother is clairvoyant and can teleport.

I'd make his power match his personality. So I'd make him brawny. Like super-strength. I know this is stereotypical, but that's what I'd do. Or, I'd make him have a wimpy power. You could make him have a power that when he plays music/sings, he can influence people.

For example, make them fall asleep, blow their eardrums out, make them happy, make them angry, etc.,