Hm, the first one is a doozy. I'll just do the second one:
A pair of trousers is something. Trousers are something.
Remember that in the first example, you are talking about the pair, not the things that comprise the pair. (People who claim to be writers get this wrong all the time, especially in music literature, when people say things lik
Actually, I think you are right about the first one: it is grammatically incorrect to say "why there's only two of you." First of all, it should be either "why, there's only two of you!" or "why is there only two of you?" The next step to making this sentece correct is, as you suggest, to make the verb plural to reflect the number of the subjects: "Why, there are only two of