It was just my guess, I'm sure about being able to play Tav and DU tho, wich was the actual answer OP wanted.
I understand why you cannot play 2 shadowhearts or 2 gales but considering DU is 100% customizable I don't see how is it any different than playing 2 Tavs, yes DU has more background but I don't see why that would prevent 2 different players play that same origin.
EDIT: Again, just what I think, I might be completly wrong.
"You are the chosen one!"
--whisper, whisper--
"Um. You are the chosen two!"
