The real Lich(First one you see) shoots 5 black orbs out at you in a fan that do about 60-70 damage.
The copies shoot pairs of green tracking bolts, and summon eyeball enemies.
Summons up to 4 copies of himself (total of 5 of him running around).
The real Lich teleports from place to place continuously. That is the enemy you need to defeat. Killing a copy spawns a large amount of tier two Bats.
Use the 4 pillars in the room to your advantage to more easily dodge his projectile weapons.
You need to continue to run and hit him even if it is just one attack. This is an attrition fight.
If you simply rush at the Lich, you can easily defeat him in under 30 seconds as the Paladin. If lives are not a concern, you can just attack him head on and lose 1-2 lives. This is assuming you put decent investments into attack and defense.
The Warlock's passives trivialize the fight. Run around the room, letting the copies summon armies of eyeball enemies, then activate your nova and lightning storm. With enough density, you will literally end up with more mana than you started with.