No workaround that I'm aware of for the parks. I'd be surprised if SS has poor bus service, given the size of the resort. Size is the prime determinant in how often the buses run. Perhaps the reports you heard were from earlier periods when less of SS was open, and the resort was therefore smaller. If not, just let your parents sit while waiting for the bus and keep your fingers crossed that the wait isn't too bad.
Depending upon where in SS you are staying, you may have an interesting opportunity to get a shorter trip from your resort to another than is usually afforded. If you are staying at the east end of SS, you'll be close (5 minute walk or so) to the bus stop for the DTD Marketplace, where you can catch a bus to any other resort hotel, eliminating the need to take two buses to go from resort to resort.