Robin&Mark, ... Please get started making your car reservation. A large percentage of cars on St. John are rented for the next year as the vacationers leave the island. You have a little more than 1 month until you arrive.
Here is an older map of the resort:
http://www.omvillasstjohn.com/images/westin_map.gif
Parking is convenient for the Hillside 2-br or less units (Buildings 31-34). But, they are called Hillside because they are perched up on a high hill (notice the switch-backs). Pools were built for each block of buildings because they are remote from the rest of the resort. Great panoramic views from up there.
If you are worried about walking on flat sand, you wouldn't want your 80ish parents walking up or down those steep hills. Golf carts are provided on a "catch as catch can" schedule by the resort. But, carts zoom around all the time. The waits are not that long to get down or up the hill.
The Hillside 3-br pool units are on the flats (Buildings 41-44). While closer to the beach, they are still a 2-2.5 city block walk to the main pool or the beach.
The newer portion of the timeshare resort (now called Buena Vista) is in Buildings 24-27. The path from Buildings 24 and 25 to the pool and beach is the flatter walk. The path to and from from Buildings 26 and 27 would be a scary walk for many 80 year olds. And, the car parking for Buildings 24-27 is next to the tennis courts. (No car traffic is allowed past the tennis courts/conference parking area - only golf carts allowed.)
The remainder of the buildings on the map are parts of the hotel. They are quite close to the pool and beach.
WSJ is a lovely place to vacation. The island is picturesque around every turn. It seems hard to get a bad meal there. I know you will enjoy it.
But, if you decide you want a car, make arrangements as soon as possible. (And, watch out for worn and under-inflated tires on the rental car.) ... eom