Just cancel the other hotels and stay at Pop, and don't stress about the cancellation fees. Don't keep beating yourself up about it! I have made plenty of mistakes in my time, and some were much more stupid and cost me much more
You are still paying less than you would have paid if you would have booked with a different airline that flies into MCO, plus you will have a car for a week. That will give you an advantage if you decide you don't like relying on Disney busses, because you can drive to the parks or to any breakfast ADR's that you have, etc. Also, if you want make a run to a grocery store to pick up a few breakfast items, etc. You might really like having the car, and you wouldn't have that otherwise.
With the credit card situation, did you try calling the card company and asking them if they will raise your limit on your one card? Maybe they would be willing to do that, since at one time they were willing to give you two different cards? That would take care of your over the limit problem, and you would only be making one cc payment.
Don't worry, this will all get worked out, and you will have a magical trip with your family