I have two characters that have finished the game, one of which I romanced with Morrigan during the game. That is the character I want to do the DLC with encase the story is different with a character that romanced with her, but he is greyed out (as is the other character I finished the original game with). I haven't done any of the other DLC with these characters.

Do I have to do other DLC with those characters before I can do Witch Hunt?

Why are these characters not usable with Witch Hunt?