One of the other named Nazgul was Gothmog, the lieutenant of Morgul. He commanded the bad guys in the Battle of the Pelennor Fields after the fall of the Witch King. I don't know the other. I don't remember that the Witch King was ever named, either.
Beregond took Pippin to the mess hall and ate with him, but he didn't give him the food.
Aragon was known as Thorongil when he served in Gondor.

How much older than Aragorn was Denethor?

JP