While sono is the verb conjugation of essere for io (I), it is also the conjugation for loro (they). In this case, since quali is a plural, sono should be refering to they instead of I. My confusion though, is that the "correct" translation seems too literal to make sense to me. I wrote down "What are they?" But well, English is not my native language either, so it could be a problem with my understanding of English......
There is a slight difference between "what" and "which ones." When you say "what are they?" you don't know what they are. You see them, but can't identify them. "Look at those round things. What are they?" When you say "Which ones are they?" you see a group of thing and want to know which objects/people out of the group. "Look at those sweaters" "Which ones?" The "What" translation of "quale/quali", from my understanding, is when you don't know what thing the person is talking about. "Look, a whale!" "What whale? I don't see one." Does that make sense? Someone, please correct me if I'm wrong.
If you ask "which ones are they," you are asking somebody to pick out a group of things from a group. In other words, you're basically asking which of the things in front of you are actually the things that you had talked about.
John and Susan walk over to a carton of eggs. "I have six eggs in this carton," John says as he points towards the full carton of twelve eggs. "Which ones are they?" asks Susan. "These six eggs," replies John, while indicating the first, six eggs in the carton with his hand.