"Are you wearing pajamas?"
I do not understand Pizsamában vagytok. Why not Pizsamákban? Many people don't fit in one pajama and there is no number before the pajama.
"Pizsamában vagytok" implies that everyone is in their own pyjamas. "Pizsamákban vagytok" would mean that everyone is wearing more than one set of pyjamas.
Yes, just as other general nouns are used in the singular (I like apples - szeretem az almát), you don't need to indicate the plural here.
Am I wrong that this sentence should be more correctly translated as "pizsamát hordsz"?
'Pizsamát hordasz/viselsz?' is gramatically correct but these 2 verbs are a bit formal so using in a context of wearing pajamas is quite funny. And I think 'hordani' rather refers to a longer time, not at the moment so 'pizsamát hordasz?' is rather should be translated as' Do you usually wear pajamas?' in that case.
better context: 'A munkában mindig öltönyt hordok' ' I always wear a suit in the workplace'
A similarly colloquial question would be 'Pizsama van rajtad?' But it is a bit more difficult to make.