Are you staying onsite? My group trip was, so thats's my only real experience with this. If you're booking room and tickets through DIsney, that's a package, which requires $200 down payment per room at booking. I'd suggest being together at the time you make the call to reserve your room and you can ask the phone CM to put a certain amount on each person's card. I'm not sure if a deposit can be put on different cards online.
You can put each person's name on the reservation(s). Once you have the room reservation, you can share your login information so that everyone can see reservation details. Each person can click the "make a payment" button on the reservation to pay their own portion up until 45 days ahead of your trip, when the full balance is due.
If you're all on one reservation, your Fastpass selections will be very easy - just click each person's name on the FP screens and choose your rides.
Youtube has some good video walkthroughs of the process if you want to see what the screens look like ahead of time. If you gave more than one reservation, with different people listed as the "owner" with theirs an
MDE account, then you just need to list each other as Friends and Family in MDE & you'll have the ability to see and make plans for each other.
On your trip, I'm not sure if you can put multiple credit cards on your room to be used for food or souvenirs charged on your magic bands. If not, you can still ask at the front desk for an itemized list of room charges and it will indicate whose magic band made each purchase. then you can add them up and ask to pay that piece of your charges with any credit card, cash, or gift card you like. Each level of resort has different spending limits before they'll automatically put everything on your credit card on file, so you'll want to make sure to do any sub-payments before those limits are reached.
Hope that helps.