Firkat, on one of our stays at BWV, we had another family with us and the husband was a large man who tired easily from walking longer distances. He was fine pacing through the mornings but getting back to the villa in the afternoons (walk/boat from Epcot & DStudios) wore him out completely. He much preferred driving his car (parked by the room) from OKW. The other 3 of us, adults, and 5 school-aged kids are just average people (not athletic) and we were okay with the midday break/walk, noting that Epcot requires a lot more walking than the other parks anyway. We were tired but it was fine. If you are going during a hot season and walking a few miles in a day is a lot for you, adding the extra walk around Crescent Lake from/to BWV may not really appeal so much to you. If you're staying at BWI or the Beach Club, it's a little closer. If your room is at the farthest end of BWV, it's a longer stretch.
BTW, if your folks own timeshare points with Fairfield, and they plan well in advance, they would have the option of Bonnet Creek. If they hoped to trade in through RCI, it's a real longshot. Bonnet Creek is heavily booked by Fairfield points owners.
With a year old baby, I'd consider an onsite monorail hotel or any location where you can park your car right outside your room.
Larger centralized hotel buildings like BW/YC&BC/AKL/WL/Swan/Dolphin and even the layout at AS/POP/POR/FWC may require you to walk some distance across the buildings/grounds to reach your car or the bus/boat waiting areas from your room. When considering convenience, note that buses do require you to take children out onto your lap, with strollers folded up during the ride. Not necessary on the monorail. Can't remember with the boats. So the disruption to a sleeping baby is still there with the bus as it is with a car/tram.
Smaller hotel buildings (even when there are several) and/or spread-out condo-style resorts may enable you to park very near your room. For onsite, consider OKW/SSR/POFQ or, offsite using a car, Bonnet Creek/Vistana Resort/Silver Lake/Cypress Pointe, etc. These are all very convenient for using your car to all of the parks except MK. With the 15 & 9 year olds, you may not be at MK any more than the other parks.
Locating your family when returning to the park after a break is just as hard/easy when staying offsite as onsite. It can actually be harder to predict when you'll get back if you are guessing how long you'll be waiting for your return bus to pick you up. With a car, you'll have a good idea of your travel time both ways, after you've done it once or twice. Cell phones help a lot when trying to get together or change/update plans.
Zalansky/Loretta, the Bonnet Creek Resort condos may be rented nightly from an owner with a minimum of 2 nights. Fri/Sat nights cost more (points) than weeknights. The seasons are not the same as DVC so your dates could work in your favor or against you. So you'd have to check the actual dates to see if this is worthwhile to you or not.
I'm not sure what Fairfield charges to rent nightly stays directly or if they even do this or not. Here's the
Fairfield website so you can locate the resort and call it, or call/email the company. Points reservations are all made through their central Owner Services so I would guess rentals could be handled that way too. Renting from an owner would be cheaper. HTH.
I was speaking more to the larger number of people who seem to have a "personal stake" in this than to any one individual. 
Firkat didn't even ask about Disney transportation.
...feel better??? 
Ya know? 
