We stayed at the Polynesian last month. Even though there were only 3 of us, I wanted to try out the day bed. I fit just fine. I'm 5'8" and I slept fine.
As far as the sinks go, I believe different rooms in different longhouses have different set-ups. Our room had one sink, in the bathroom proper. Just like at home. Two sinks would have been nice but I'm not complaining. We liked the Polynesian and would love to stay there again.