To use Disney's Magical Express (DME), it's necessary to be on a reservation for a Disney-owned resort hotel at Walt Disney World.
I see that you're staying at BoardWalk Villas. How many people? What kind of villa?
Let's suppose you're a family of 4 staying in a 2-bedroom villa, which officially has a capacity of 8. Now let's suppose your friends are also a family of 4. The dates of their Swan reservation fall within the dates of your BoardWalk Villas reservation. You could add them to your reservation as registered guests "staying" in your villa. They could use DME. They could even use the pools at the BoardWalk. Their villa key cards can be made without allowing room charges. You would be within the occupancy limits, so you're within the rules. (A registered guest is not required to sleep in the room.)
Your friends could be on your reservation for your whole stay. If it's a DVC reservation, there's no charge for extra guests, even adult guests. There's just an occupancy limit. And you need to provide the names of all guests that will be registered guests for that DVC villa. (All this assumes you're not using the
Disney Dining Plan or any other paid Disney service that applies to everyone on the reservation).
The DME system is sophisticated enough to allow guests on the same reservation to arrive on different flights, even on different days, as long as the arrivals are within the reservation dates. So if you're using DME on October 13 and they're using DME on October 16, it's not a problem for DME.
HOWEVER... if the math of total guests vs. maximum allowed occupancy does not work out, then this is not an option.