If they are staying at the All-Stars they will get a parking sign (to park in All-Stars). That is good to go and park at the other resorts. Two years ago I stayed at the All-Stars but went to Poly, parked and had no problem (went to dinner then watched the fireworks from the beach).
Why add extra trip when they could just drive there. That is if they are going to have a car. Otherwise taking the bus to MK then the monorail to Poly is the only "free" way. Enjoy!