Characters who hate.

My characters don't like each other and it's kind of frustrating.  I don't know how to make them like each other.

Do I just put them in a room and leave them there together until they sort it out?  I'm trying to write a romance here but these two bastards aren't cooperating!  I don't think I'm asking for much.  Just some civility which might bloom into some kind of respect and eventually deepen into affection and love.

Instead it has to be all like, "You tricked my brother into fairy and now he's lost!"

"You've kidnapped me for my magical wish granting skills - sucks to be your brother!"

"Evil demon harpy!"

"Medieval moron!"

Then I try to avoid them killing each other and prematurely ending my novel. 

It's worse than having children!