You’re not supposed to survive against 3 players beating on you at once.
But if that’s what you’re after, go play in CP Cyrodil and find some newbs to fight; preferably close to a tree.
mighty chudan...impregnable...fortified brass...transmutation...most if not all classes have access to a 5,280 buff for their spell and physical damage resistance - slot that...
grab a resto staff, slot combat prayer...
figure out your burst and heal over time...
try 2 pieces of heavy armor...2 pieces of heavy chudan, combat prayer, plus class resistance buff will definitely help you stay in the fight...
Pirate Skeleton helps with light armor.