This is a broad question, but I'll do my best!
Hotel: If you want a value, I definitely say Pop Century. It's my family's favorite hotel. It's very upbeat and fun, the pools are nice and the food court is amazing. Word of warning, if you're family isn't much into bright and colorful or really needs peace and quiet, I don't think this would be good. The rooms are smaller, there are a lot of kids and a lot of people stay up late, so it can be kind of noisy. I know a lot of people hate the bright theme and think it's tacky. I've never used Disney transportation so I can't say much for the buses. We have 4 people each vacation and the rooms are always clean and big enough for us.
We've only stayed there All Star Movies and Port Orleans: French Quarter. All Star movies was quite awhile back so I can't say how it is now, it was fine then. We stayed at French Quarter last summer and we loved it. We got a room that hadn't been refurbished so the room was not great. That said, the whole theme is beautiful and the rooms are bigger. I loved walking around and looking at everything. You can also take a boat at the hotel to Downtown Disney. It was very relaxing and awesome to be able to hop on a boat! The food court is okay, try the beignets if you go. It's quiet and I hardly saw many people there when we stayed last summer.
As for the smell at AKL, one of my friends stayed there in September and said her room smelled bad too from the animals outside.
Rides:
Since you have quite a few people going, you can pretty much hit up whatever you see that looks fun. From my knowledge, your cousins should be able to ride everything since it's height related. Some rides might not be good for the 64 year old depending on health.
Magic Kingdom:
Astro Orbiter: Never been on this, but appropriate for all ages. Basically just spaceships that lift into the air and circle.
Big Thunder Mountain Railroad: One of my favorite rides at Magic Kingdom. Should be fine for everybody. Goes pretty fast, no loops.
Buzz Lightyears Space Ranger Spin: Fun for everyone. Slow, in the dark, shoot targets.
Might get a fastpass early, this line can get pretty long.
Dumbo: Depending on the kids, they might think it's too childish.
Haunted Mansion: In the dark, might be scary for a 6 year old, basically just ghosts, but it's fun and goes slow.
It's a Small World: Everyone can ride.
Jungle Cruise: Fun for everyone.
Teacups: Adults seem to not like the spinning so it might just be fun for the younger crowd. Fun for everyone.
Magic Carpets of Aladdin: Basically like dumbo and astro orbiter, depends on the kids.
Adventures of Winine the Pooh: fun for everyone.
Also Fastpass is best idea.
Peter Pan's Flight: Fun for everyone.
Suggest getting fastpass early in the morning, the line gets long.
Phillhar Magic: 3D show, fun for everyone.
Monsters Inc. Laugh Floor: Fun for everyone.
Pirates of the Carribean: Some loud sounds, should be fine with everyone.
Snow White's Scary adventure: I think this will be closed next summer, not sure. Scared me when I was a kid, but it's slow and I think the kids will be fine.
Space Mountain: In the dark, fast, 44 inch height or taller, not sure about the 6yrold. Fun for the older kids.
Definitely get a fastpass, this ride seemed to have the longest lines all the time.
Splash Mountain: Should be fine, steep drop into water.
Stitch's Great escape: Should be fine, not my favorite.
Tomorrowland Speedway: Fun for everyone.
Epcot:
Mission: Space: 44inch height. Not sure about the kids, probably just teens and the adults, not sure about the older adults. You can pick the milder side of the ride. I haven't been on it because I'm afraid of it. haha. My family has been on it and said it was fun.
Soarin': Fun for everyone. If someone is afraid of heights, they probably shouldn't ride it.
Fastpass this.
Test Track:Should be fine, goes fast and sudden turns, not sure about the older adults.
Fastpass this if possible.
Seas with Nemo and Friends: Fun for everyone.
Disney's Hollywood Studios:
Great Movie Ride: fun for everyone.
Muppets 3D: 3d movie, fun for everyone.
Rock 'n' Roller Coaster: 48 inches or taller. Probably not the 6 year old or the older adults. Loops, dark rollercoaster, fast takeoff. One of my favorites.
Tower of Terror: 40 inches or taller. Not sure about 6 year old or older adults. Fast drops and sudden drops. Another favorite.
Toy Story Mania: 3D game, fun for everyone. Favorite.
Definite fastpass. Get there first, grab a fastpass then get in line to ride. This is the longest line at WDW right now I'm pretty sure.
Animal Kingdom:
Dinosaur: Never been, but I'm thinking everyone should be fine. Kind of scary with dinosaurs.
Expedition Everest: Not sure about 6 year old. I think it's the scariest ride in WDW. Fast Rollercoaster. Still a favorite.
Fastpass this.
Tough to be a bug: 3D show, fun for everyone if they're not afraid of bugs.
Kali River Rapids:Water ride, should be fine with everyone.
Kilimanjaro Safari: Fun for everyone.
Primeval Whirl: Lots of twists that gave my family a headache. Should be fine for everyone.
TriceraTop Spin: Like Dumbo, depends on kids.
http://disneyworld.disney.go.com/attractions/?fv_78193=on&resultSet=42page=2 Here is a link that lists all the attractions at all four parks that you can look more into. It has height listings and with some pictures which will help decide.
If you're not sure about some I suggest looking them up on youtube and it'll give you a good idea about whether they're appropriate for the kids or older adults. I don't know that many 6 year olds so I don't know whether they're too scary or not.
Hope this helps!
ETA: Added some things about fastpass. It's best to get there as soon as the park opens and hit up a fastpass for the ride you want to ride the most, then hit the line for another ride you want to ride. You can knock out two pretty fast. Your family probably knows about fastpass. If you'd like to know more I can explain it!