Book a cabin for three (a TBD person as the third passenger which you cancel before final payment) - it is sometimes a lot cheaper than two and maybe cheaper even than a GTY booking.
None of that matters. As you discovered the pricing is dynamic. Even if someone has seen it lower on another ship/sailing - it likely won't affect what the price is for your sailing.
As mentioned, the shows listed in the app now are the ones that are very likely will be on in Dec. For context, shows typically don't change but maybe every ten years during a dry dock typically - none of that will happen between now and Dec.
You'll have to give up your laptop sharing and have the two devices you use around the ship bump all the other devices. Or, if you are together all the time and one of your devices can share a Wi-Fi signal, do that with one of the devices.
Welcome to CC and coming out of lurk mode.
You'll probably need to ask one of the shuttle services if they provide car seats. Also, ask in the Florida departure section of CC.