"Da" can be used to refer to any location. It simply means there or over there.
So in response to your first question - yes.
In response to your second question: Das is used to ask about any person, gender doesn't matter.
Wer ist das?
Means who is that? You don't need to specify whether it's a man or a woman you're referring to. It works for both sexes, and that's why you don't need to further distinguish between to the two. You can, but you don't need to.
If you want to ask about multiple persons, you'd go:
Wer sind die da?
However, when referring to a group of people you commonly further clarify that, as in:
Wer sind die Leute da?
Again, you don't need to do that though.