Hello! I´m Luz. Could I ask you some doubts?
1) When my boyfriend and I picked them up from the terminal, there were cries, laughs and hughs.
I know that "laughs" is used incorrectly, but I don´t know why. Could you explain it to me?
2) If there´s someone at the door, is it correct to say: Who´s that, please?
1) It would be better if you say tears, laughter and hugs because they are all unambiguous nouns. This is what we English teachers call parallel structure.
2.) We usually say "Who's there, please?" or "Who is it?"
By the way, the word laughs can be either a plural noun or a third person singular verb. Examples:
He laughs at my funny hat.
I get lots of laughs every time I wear it.