As above, I would expect "normal rules" to apply if the flight is operated by Virgin Metal on a code-share.
So DS Check-In free of charge if Upper Class / Flying Club Gold / on a Virgin Holidays booking (although unlikely VH would book you on a code-share). $10 per person charge otherwise.
Ask yourself what your plans are for the final day, as Disney Springs check-in is not ideal for everyone. All of your party have to be present at DS check-in to check bags / have passports checked etc (so possibly not ideal for some families). If you've got late check-out on your hotel room / villa & you don't need to leave bags on view in a parked car during the day, it may just be better & easier to check-in at MCO (still do OLCI first though, so sort of lock-down your seat selections). Drive up to departures drop-off area and unload the car + bags, then have the driver return the rental car & meet the rest of the group in departures before proceeding to check-in.
For us, Disney Springs check-in works well, as we have to be out of our hotel room by 10am. Check-out, drop bags at Disney Springs & then head to Islands of Adventure for the final day & a good lunch at Mythos, before making the journey to the airport (via either our hotel or Aquatica for shower facilities). Remember - you can do both Disney Springs & airport check-in if you need to drop an additional checked bag at the airport (subject to baggage allowance, obviously).