From Ohana's to the MK will be simple... Just take the Monorail. When you leave the party... I'm not sure where you will be going, but don't worry, we'll get you there!
Both the Monorail and watercraft will be in operation for the entire Christmas Party... watercraft will run 45mins after the party ends, and the Monorail will until everyone is gone. (approx 2hrs)
A note: The launch boats to the Poly/GF are NOT accessible... To reach the Co/Po/GF you would have to take the Monorail.
The ferryboat to the TTC/parking lot is completely accessible... the gangway only has a slight hill, and the lower level of the boat allows plenty of room to move about. One thing to note about the Ferry... at night, it might get a lil windy and chilly... so you might need something to keep warm on the 5min ride. It does make for a very relaxing, peaceful, and pretty ride at night...
The Monorail is also completely accessible for your sons wheelchair... however... I will warn you... there is a large ramp to access the monorail (since it is elevated), and there is no elevator. One monorail is Express to the Parking Lot... and the other monorail is for Contemporary, Polynesian, Grand Floridian. Please make sure to read the overhead signs at the entrance to the Ramp, to make sure you get the correct one, if this is what you need. Don't want you to go all the way up the ramp only to find it doesn't go where you want it to go!
Enjoy the party!