为何用 Those are...来回答 Who are...

Who are the boy and the girl in front of Paul?

为何用 Those are Paul's son anddaughter,my cousins,Mike and Helen 来回答？

为何用those are回答？

你也可以用 they are。  就好比你回答 What's this？你可以说 It's a pen. 也可以说 That's a pen.  that 和 those为远指代词，指代离说话人比较远的人或事物。