Why isn't this bersama-sama as it refers to two people?
Is bermain also used to indicate playing an instrument?
No, because "bermain" is an intransitive verb (it has no object).
It's enough to use the base word "main" (to play) , something like this :
"Saya main biola."
But you can say "saya bermain musik" right?
Bersama vs Berkumpul?
berkumpul = to come together, to gather
Why would "we are playing together " is a wrong answer
So i use "main" with an object (like a toy) and bermain with no object?