The three resorts (Sheraton Vistana Resort, Marriott's Cypress Harbour and the HGVC at SeaWorld) are all very nice timeshare resorts. I'm not sure when the SeaWorld HGVC was last refurbished but the other two are right up to date with refurbs over the past few years.
All three have nice resort amenities - pools, hot tubs, tennis courts, playgrounds, fitness room, resort stores, bar & grill, etc.
All three are well located for a variety of Orlando-area activities, restaurants and theme parks.
HGVC SeaWorld, as the name suggests, is in the SeaWorld neighborhood - across Central Florida Parkway (and walkable) to the theme park. It's also quite near an I-4 entrance/exit for ease to get to Disney (a little further from an I-4 entrance to go east toward Universal).
Cypress Harbour is also in the SeaWorld neighborhood a short distance beyond the HGVC on Westwood Boulevard.
Vistana Resort is in the Lake Buena Vista neighborhood just off SR 535 and close to two I-4 interchanges.
Yes, Vistana is closer to Disney than the other two but the difference is not significant. For instance, it's about 7 miles from Vistana to Epcot, from HGVC SeaWorld it's about 9 miles and from Cypress Harbour it's about 9 1/4 miles (distances will vary a little bit based on where within the resorts that you stay). So the travel time difference between the closest and the furthest is probably around three to five minutes.
For us the size of the villa at a resort is important - we like space. We've stayed in a three-bedroom villa at HGVC SeaWorld and the two-bedroom portion of that unit was pretty big - probably the largest of the three resorts. The Vistana units that we've stayed in were definitely the smallest - probably in the 1000 to 1200 square feet range - of these resorts but there's variation in size between Vistana sections (the newer phases were built with smaller villas than the oldest sections). The villas at Cypress Harbour are all two-bedroom units and are a standard 1345 square feet.
I like the resort layout and landscaping best at the Marriott resort. It makes for a nice, laid-back atmosphere - seemingly less hectic - and the layout is compact enough so it's pretty easy to walk from point to point for all the resort services.
I think that all of these resorts would give your family a really nice vacation experience and I wouldn't hesitate to stay at any of them. However, Marriott's Cypress Harbour is our favorite Orlando timeshare resort and we'd stay there over the others if we were faced with the choice that you're faced with.
Enjoy!
Dick Taylor