It would be really helpful to have an explanation from an Italian speaker. Does Italian always uses the plural pronoun quali with plural nouns?
In English, we use the interrogative pronoun what with plural nouns when asking for various types of information: ""What are your names?" "What places have you visited"? "What are the facts?" The interrogative pronoun which is used more narrowly to emphasize a part of a whole or a subset of a group: "Which name did he choose?" "Which places will you visit tomorrow?" "Which facts support your theory?"
Does Quali sono i numeri? signify a similar emphasis on a part of a whole or a subset of a group? If not, "What are the numbers?" would be a more natural English translation.