Complex sentence: After the battle he comes home, unintentionally walking in on his mother, Greg having sex and erupts between him and Greg, which inadvertently wakes Lily, whose presence immediately quiets Jimmy's anger.
Split into simpler sentences: After the battle he comes home, unintentionally walking in on his mother and Greg having sex. Afterwards an altercation erupts between him and Greg, which inadvertently wakes Lily, whose presence immediately quiets Jimmy's anger.