##Answer no longer valid after edit

They are
>! 6, 3 an 2

Because
>! 36 = 36*1*1 = 18*2*1 = 12*3*1 = 9*4*1 = 9*2*2 = 6*6*1 = 6*3*2 = 4*3*3  
>!  
>! I assume every body is older than 1 (because the youngest can play piano)  
>!   
>!  $36 = 9*2*2 = 6*3*2 = 4*3*3 $  
>! There is a youngest daughter (there can't be 2 youngest daughters) so they are 6, 3 and 2

But :
>! - You can be younger even if you have the same age  
>! - I don't know any 2 years old girl who plays piano