Looking up Wikipedia, it actually looks like Cave Dwellers (A.K.A. The Blademaster, A.K.A. Ator 2, l'invincible) is next in this series, and then there were two competeing third movies. A new director made "Iron Warrior" which flat out contradicted the entire Ator backstory, then the first director made another one ignoring Iron Warrior called many different titles (Ator III: The Hobgoblin, The Hobgoblin, and Quest for the Mighty Sword). This actually featured the son of Ator, and is the only O'Keefe-less Ator movie.
Also, the hobgoblin in question reused a costume from Troll 2...so wow. It was even called Troll 3 in Germany.
From the movie itself, I learned that romance with your not-sister seems exciting, but short-lived, since she's gone by the next movie and replaced by a guy named Thong.
I also learned that caves are mostly just cave entrances and greenhouses.