It's fitting that you'd fight the Skeleton Lords in a room made of bones. When the encounter begins, three large skeletons (the lords, presumably) assault you at once. Together, they--as well as the skeleton minions they summon--share one giant health pool.
Try to knock out one of the melee lords first, and make good use of the giant bone pillars to block the mage's attack. Need more tips? Check out the video above.
For more help be sure to check out our complete Dark Souls 2 Boss guide.