Joel
Platinum Member
You will not be charged extra if you booked with two and showed up with 4 as long as your room can accommodate 4 people. Meaning if it only has 1 king or queen in the room that would be a problem. But if you booked a room that has 2 queen beds in it. You will not get charged extra. At all. They will ask how many room keys you want when you check in.
Most hotel rates in the US are based on double occupancy. If you look at the fine print when booking, you can be subject to extra fees for more guests. Most hotels are very lenient about them, some are sticklers. I can see Cabana Bay and Sapphire Falls being lenient because Express Passes aren't available at those hotels, but I wouldn't be surprised if you see the fees at the other three hotels.
Essentially, YMMV.
All Universal Orlando Resort Hotels do NOT charge for any additional guests, unless they are over the maximum as @darkridelover said. Also, they only make one person in your family have their room key out when going through the early access check point (they say that as you're approaching so they don't clog up the entrance). We've actually used an old key from a previous trip to get in before (before AP received early entry).