We have had a time when the hotel had only a king bed available for our family of four. Luckily our kids were 2 and 3 so we all just shared. I have heard of it happening to other people also. So, be prepared for this to happen.
But, I don't think it will be a problem in Orlando. We still use priceline for our family of 4 and cross our fingers. The savings we have had over time exceed what we would pay if we encountered a problem.
Also, once this happened to a friend, and the hotel offered to bring in a rollaway, but they would have to pay RACK RATE!!!
I am sure every hotel has it's policies, but I am pretty sure most are customer service oriented and will do their very best to accomodate you.
Good luck!