I would say this should be correct as well, since we are missing the context..
Nope, suonare can only mean playing an instrument, never acting; that's "recitare due parti".
Two "parts" is in their own suggestion list and it does make sense: once big pieces of music consists of different parts. The problem with Duolingo is I spent as much time guessing which translation they accept as finding the meaning of the Italian phrase.
The girls played two pieces is marked wrong. A musician can play a piece (of music) or he can perform it which requires an audience.
Haha, that happens when you get thrown in. I guessed "The girls rang twice." and constructed the context of ringing at the door. It turns out I guessed wrong :-)