I can't comment on the seats, but I would recommend flying to TPA instead. Immigration at TPA is very very quick and the car hire is on site I have flown into TPA loads of times and MCO just a few. It takes around an hour from TPA to hotels in Orlando, I think it's quicker Flying to TPA and driving across then the queue at MCO another option at TPA is staying at the airport marriott for the first night can be worth thinking about with little kids, the hotel is in the airport building and it takes about 20 mins from plane door to hotel room.
Have a great trip.