"To sing with a man is hard."
Translation:A cânta împreună cu un bărbat e greu.
Does the word "impreuna" always appear with the word "cu" that is, in any, each and every context?
It does not say together in the english sentence. It just says with. So only "cu" should be correct.
Bărbat means man, in the male sense.
Om means human, it's a masculine noun, but it can referrer to both male and female. It is often used to refer to an individual. Its plural is oameni.
So for this translation, as the English man can both mean a male or a human, it can be translated as both bărbat or om based on what you really mean.