As PP said, there is a Disney ticket desk there to buy park tickets. And as far as I know they do not charge for extra people in a room. We're a family of 4 and have always stayed without an extra fee. Of course, Dad is a Starwood Corporate employee, but the only hotel he ever told me to "hide" someone was at Caesar's Palace where apparently they DID charge for extra bodies. You should be 100% fine at the Dolphin. Although, it doesn't hurt to call and double check.