Here's the short answer: yes, there are buses that run to the expo from the resorts on Thursday, Friday and Saturday. I don't know how often, as I've always driven over to the expo, but I would assume it would be at least every half hour or so. And you are correct, there are NUMEROUS buses that run from the resort to the races on Saturday and Sunday morning. They start about 3:00am. Racers are supposed to be on them by 4:00am, but honestly, I would assume you could push 4:30 or 4:45 and still make it to the start. Spectators can also take the buses, which run throughout the morning between the resorts and Epcot. The roads can get congested between about 5:30am and anywhere between 8:00 or 1:00 for the full or half marathon, so I would advise them to get on a bus early if they want to watch you.
If they can get to the monorail, it is BY FAR the best method of transportation on race morning for spectators.
I'm sure others can chime in with all sort of tips.
Hope that helps!
Steve