I arrived at Mankar Cameron's throne in his Paradise, but he isn't there. His two kids come in and stand on either side of the throne and just stare at me. All of the doors are sealed, and those two just keep spawning if I decide to kill them.

I think this might have happened when I went to the Mythic Dawn cave near the beginning of the main quest, I tried very hard to kill Mankar Cameron. He ended up disappearing, I never saw him open the portal to leave.

Anything I can do?

open the console and type

Don't you mean "placeatme"?

Whoops, a bit of dyslexia set it, happens to the best of us!