Just circle with them and keep your shield up, or roll away from their attacks if you can. Their semi-invisibility can make them hard to spot at first but once you do it's easy enough to keep your eye on them. Try to pull one enemy at a time.
You should be able to block their attacks then just strike back when there's an opening. They're honestly mostly like any other enemy with the only difference being you can't lock on. Just use your camera and you should be able to stay in front of them.
Don't give in to using that pathfinding cliff glitch thing on them.

They can drop some loot and generally don't respawn. There's also a semi-invisible archer further in the back who drops a very nice bow, but he's near the edge of a cliff and can easily fall off since he likes to roll a lot and get in longer range. He also doesn't respawn so if you want that bow make sure he doesn't fall off.