"Are these the clothes of someone?"
Translation:Hainele acestea sunt ale cuiva?
When you have the article "-le" at the end of the noun in a possessive clause like "someone's clothes", you mustn't use the possessive pronoun "ale". It sounds weird and redundant if you do (and is incorrect).
So your translation should be:
"Are these someone's clothes?" = "Acestea sunt hainele cuiva?"