The older girl is the younger girl's big sister, not her mother. She calls her "onee-chan". They were a sort of parallel to Citron and Eureka.
People who think it is unbelievable for Cameron to be strong because he is this idiot kid clearly have not been viewing anime properly.
Anime has proven that characters don't always have to be geniuses to win in a battle, for some people brawns is what works for them.
In fact, Cameron is basically just another Ash. Ash too is dumb, the main character, the guy you're always rooting for.... DO YOU SEE?