Don't worry you don't need any of the legendary to get Kyurem, although, you would need only ONE of them if you'd like to fuse Kyurem and (said legendary) together.
It's "too late" for me... I started a white party.
Thanks for your answer about Kyurem. I don't really know this pokémon. But a Dragon/Ice. It's amazing, so I want him to try a third team. (Reshiram/Kyurem/Zekrom).
Well, as I started the game three days ago, I'll continue, it's also to catch the pokemon, I could only find on white to trade them to my black party.
Of course, I'll trade Zekrom... Even if I don't like too much his attacks, I find that he has THE dragon style.
A thing which would be good; it's because the legendary has nothing to do with a version of game (black or white), but indeed with actions. There would be characters who would ask for help them and according to the answers and the results, we could claim the one or other one of the legendary.
When I've had the Idea to buy the game, I visited the am*z*n (no pub for) website and after 20 minutes of hesitation, I bought both.
I did the same thing with HG and SS. And, I think I'll do the same if I buy B2/W2.
Because it's very hard to decide from a picture. Seriously, WHO bought the game for legendary with the picture ? For me, If I don't like the legendary it's not interesting to have the game.
I imagine a little boy (or girl) in front of his/her parents who offered a white or black version while this child wished the other version.
Parents as mine aren't nasty, but when I was a child, I indeed had to insist to have the good game. (Because they nothing know about videogames). Even if, I admit that sometimes, they brought back to me some good games without realizing it really themselves (on Nintendo, it was long time ago).