Is the expression "Who are those?'' used or is it only "Who's that?'' and "Who are you people?''?
If there is more than one person, then "Who are they?" would be appropriate. "Who is that?" refers to just one person. "Who are you people?" sounds rather abrupt and rude to me and it would be directed at those people that "you people" refers to. The first two would be directed to a third party.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.