Neither of them knew they were related. Firestar and Scourge were half brothers (same dad, different mom), so they didn't know each other until Tigerstar brought Bloodclan into the forest. Before he was Scourge, he was named Tiny because he was the smallest. His own litter mates had fun of him. One day, he just snapped and kill everyone in his litter. Later on, he formed Bloodclan, where Barley was forced into doing Scourge's bidding, killed Tigerstar, and was later on killed by Firestar.