"Whose cups are those?"
Translation:Di chi sono quelle tazze?
I think in this case 'quei' is a plural demonstrative adjective that modifies 'bicchieri'. The word order makes it confusing. To use 'quelli' the sentence might read > Whose are those? = Di chi sono quelli. Without a noun to modify, 'quelli' becomes a demonstrative pronoun. See http://www.angelfire.com/bc/vanoni/italiano/grammatica/demonstrative_adj_pronouns.html for more than you ever wanted to know about this subject!
I answered, wrongly with, "Di chi tazze sono quelle?" I'm guessing this is a word order issue. Could someone give me some guidance as to why, please?
The English "whose" and the Italian quel... generally precede the word they modify. Your problem is that you tried a literal translation where di chi would be the modifer. But it can't be: it's like saying "of whom's cups are those?"