Well, let's see... we have a pool of 2000 possible people to choose from. For the sake of convenience, we can imagine they're wearing number plates with the numbers 1 through 2000. Of these 2000 people, we're choosing 1000 of them. That much I follow just fine. I concur with Stapel that everything after that is nonsense. Some specific questions you might answer:
You mention "candidate A [and] B" but which of the 2000 people are they? If each of them has a 0.5 (or 50%) chance of being selected, then that means that none of the other 1998 people can be chosen (as their chance is, by definition, 0%). So, how can you expect to choose 1000 people, if only 2 of them can ever be chosen? And then that last bit is a total disaster and I can't even guess as what might be meant by it.