Hi Kim!
Well, I am so sorry it took so long to respond to you. With the addition of the new race, I wasn't sure what runDisney planned to do with the extra race days.
The official answer is "maybe"! The plan is to have the monorail running early enough for runners to use it all four days of racing. BUT, the transportation schedule for that weekend is still being worked through and developed, so it isn't set in stone just yet. I would think that your family will be able to take it for sure, but it may be that runners will be using buses only.
As the race gets closer, they will finalize all of these details. You will be able to find them on the
Walt Disney World Marathon weekend website, and they will also be in the Final Race Instructions booklet that will be available for download online and in print-form at the expo.
Of course, please feel free to check back here with me. If I don't know the answer, I can certainly find it out!