Kidani. The third bathroom will be very handy. Nice pool and water play area for the little ones. While the bus from Kidani feels like a long ride it really isn't too bad and not much longer than other rides.
All three resorts have a community room, make sure to stop by!
Kidani. Three bathrooms make it more comfortable with 4 adults. The kids’ splash and play area is great. Long hallways mean that it can be a bit of a AKL to he bus stop but at least the walk is indoors whereas SSR and OKW bus stops are an outdoor walk away from the villas.
However, OKW has full size washer/dryers in their villas and they are the most spacious of all DVC resort villas. That might trump the extra bathroom and indoor hallways at AKV for you.
Another vote for Kidani! I think your 2yo and 5yo will love the pool and splash areas. There will still be a lot of walking for the 74yo, but at least it will be indoors and it does not involve riding the internal bus loops like at OKW and SSR.
The lunch and dinner food options can be limited for picky eaters at Kidani, but you will have the full kitchen which offsets that small issue.
Kidani has 1 bus stop. Buses are shared with Jambo House, which has 1 bus stop.
I believe SSR has several internal stops before you leave the property. I'm not sure about Old Key West. If you're not used to being at a resort which has many internal stops, you might not like it.
OKW has multiple bus stops for the theme parks (in this order, Peninsular Road, South Point, Turtle Pond, Millers Road, Hospitality House). There is a nice boat ride over to Disney Springs. Most of the buildings at OKW do not have elevators. Would your 74 yr old have difficulty taking stairs? You might need to request a first floor or one of the three buildings with an elevator for medical reasons.
Another Kidani vote here. The third full bath trumps all else, in my opinion. AND it is a lovely resort. There is a shuttle that runs between Jambo and Kidani from early morning until 10-11 pm. When considering the internal bus stops at your other two choices, Animal Kingdom Lodge buses are probably shorter ride lengths.