Roxy Wellard is clearly the brains of the family as most of the schemes are thought up by her, because of her small size and the fact she never fights we can assume that she is a bad fighter. Which would be the reason why she uses her brother Rio for such things. Since Rio mentions "All our dads" it is implied that they share the same mother, but not the same farther.
Roxy has occasionlly been nice such as when she teamed up with the other kids to rid the Dumping ground of a social worker who was very strict, (The kids were unaware of this suggesting Roxy is a good judge of character). She also is a rival with Tracy, largely becuase Tracy is immune to her intimidation and the fact that Tracy is aware that she uses her siblings as muscle. But they have had some good moments, such as when Tracy comforted her over the deprature of her sister. Chantel left because her dad wanted her back.