Hello~!
(This was originally a reply, but it wasn't showing up)
I checked the credits from the Season 3 premire and it turns out that Brianna Gentilella is the only member left from the original main cast (aside from Tino Insana and Chris Phillips). I'm assuming that she only sings for Molly now. I made a list of all the new voices and did I little web surfing to see who plays who. I wasn't able to find out what parts of the characters they play:
Gil-Jacob Bertrand (Speaking?)
-Teddy Walsh (Singing?)
Molly-Baliey Gambertoglio (Speaking?)
Goby-Marleik Walker (Speaking and singing?)
Deema-Grace Kautman (Speaking and singing?)
Nonny- Jet Jurgensmeyer (Speaking and singing?)
Lil' Fish-Mia Vavasseur
And I'm guessing Tori Fensten is Oona. I couldn't find who she played, just that she's in the show. I'll admit, I was a little sad when I found out that most of the voices were replaced, but that's what happends when an young actor's voice changes...or they want to move on...or their contract expires. The voices are very close and fitting though. I thought Deema's VAs were still there at first, just with maturer voices. I had to listen really close to hear the difference in Gil's voice.
I think the new cast is doing fine and will get better later on. Bye~!