Carlos was the one who brought Judo or what Brazillians called at the time Kano Jiu Jitsu to the Gracie family and they all collectively tweaked it and created Brazillian Jiu Jitsu. Helio just become really famous because he was more active in promoting it through prize fighting and competitions and because his sons we're all really famous. In terms of who created the system it was pioneered really by both of them. Helio's whole goal was spreading the art while Carlos was more traditional teaching it to family.