Complex sentence: Peace on the farm is maintained until zombies manage to break free from the barn and kill several members of Hershel's family which, again, prompts the group to continue their search for yet another safe haven.
Split into simpler sentences: Peace on the farm is maintained until zombies manage to break free from the barn and kill several members of Hershel's famil. Eventually the barn zombies escape resulting in the deaths of several Greene family members and again prompts the group to continue their search for yet another safe haven.