If you want to get to Fort Wilderness by boat, then yes, you need to park at the TTC, then monorail or ferry over to Magic Kingdom. Then you would take the boat from Magic Kingdom to Fort Wilderness, then a short walk from the marina to Pioneer Hall. YES, this boat is accessibile!!!
HOWEVER, getting back to TTC may be a problem if you are at one of the later Hoop De Doos if the MK closes early. There is no easy accessible way to the TTC if the MK is closed.
What you could do is have one person in your party, after dropping the rest of you at the TTC is drive the vehicle over to Fort Wilderness. (Use the public day lot). Then that person can take a Yellow, Purple, or Orange Settlement bus to get to Pioneer Hall.
OR you could all take your car over to Ft. Wilderness, but get there a couple of hours before the Hoop De Doo, then take a bus to Settlement, then proceed to the marina and take a round trip boat ride to Magic Kingdom, OR if your person in an
ECV can walk a few yards, you could leave the ECV parked near the marina buildings and take a roundtrip boat ride to Contemporary and Wilderness Lodge, then back to the Fort.