Well, there is healing magic: when you drink potions or eat meals, your bars magickally rise up again fast. It just that it's not instant.

You have weapons that work fine against undeads.

In co-op, you could be the character who tosses potions at friends during fight, but frankly, with such huge inventories, everyone can store potion and meal before fight. You could instead be the one who actually works to prepare potions and meals for other who specialize in other duties (collecting resources, building, etc). It isn't any actual specialisation (no skill improvement), but RPG specialisation (actions you do in game).

There are no offensive auras, but they can be "tank"/aggro roles, although these will require a fairly high playing skill (how to dodge and parry, how to position, etc).