Most rides can fit 3. I went on pretty much everything with my DD and DH. Although, DD is very skinny! The only exception was Barnstormer. The 3 of us couldn't fit, so I sat by myself behind them. We even squished together on Dumbo.
I agree, the only rides where the three of us (DH, DD9 and I) couldn't get on together was the Barnstormer, Splash Mountain and Big Thunder. Everything else, we were able to ride 3.