Bersama and bersama sama is same i think
The only defition for bersama-sama in kbbi is "bersama" so yep
Can any native speakers give any insight on why one would be chosen over the other?
I'm guessing that bersama-sama involves a bigger group.
We use "bersama" as it means "with", we use "bersama-sama" as it means "together".
So after "bersama" follows an object (person), and after "bersama-sama" not?
I think the appropriate one should be "bernyanyi" instead of "menyanyi".
Attention Duolingo: You have fixed this translation here in the discussion, but you have not fixed the multiple choice option, which still has "menyanyi" instead of "bernyanyi".