I have a b-kyurem would it work to trade it over to my other game and then fuse the next kyurem I get in the b2 game fuse to get w-kyurem and trade the b-kyurem back over and have both forms
No, as the DNA Splicers is a Key item, thus not being able to transfer Kyurem-Black or Kyurem-White.
Yes, because if you disfuse them, you could trade them seperate. Just refuse them once the trade is over. (Heres some extra info.) The reason why you can't trade them fused is, the game makers don't want you to trade two Pokemon for one.