Most of the lines are Mainstream Lines, which are wheelchair accessible in the regular line. There are very few separate 'wheelchair lines', most of them are in Magic Kingdom,which is the oldest and least accessible park.
Most attractions for all parks are listed as "Enter through standard queue" for attractions without Fastpass or "Obtain a FASTPASS OR use Standby Queue" on the Guide for Guest with Disabilities maps I picked up in October 2009. There is also a large red box on the maps which says "Guests with any mobility or queue related assistance needs are encouraged to use the Disney's FASTPASS option wherever possible." There is the same explanation about how to use Fastpass as on the regular park maps.
These are the attractions in each park with a different method of access listed on the map:
MK
- WDW Railroad: Enter using ramp on the RIGHT on Main Street
- WDW Railroad: Enter using wheelchair ramp on RIGHT at Frontierland
- Big Thunder Mountain RailRoad: Obtain Fastpass or see Host for options. If FASTPASS is not available, enter thru access on RIGHT
- Country Bear Jamboree: Enter thru door on LEFT
- Hall of Presidents: Enter through door on RIGHT
- Liberty Square Riverboat: ENter through exit on RIGHT or LEFT
- it's a small world: Enter thru standard queue. Follow directional signs to designated load area
- Peter Pan's Flight: Obtain FASTPASS or see host for options. If Fastpass is not available, see a host for options.
- Snow White's Scary Adventures: Enter through Exit on RIGHT
- Cinderella's Golden Carrousel: ENter through exit on RIGHT
- Dumbo: Enter using ramp on RIGHT
- Tea Party: ENter through exit on RIGHT
- Barnstormer: Enter through exit on LEFT
- Space Mountain: Obtain a FASTPASS or see a host for options. If FASTPASS not available, enter through queue on RIGHT
Epcot
- Spaceship Earth: Enter through the exit on the RIGHT or LEFT
- Gran Fiesta Tour Starring the 3 Caballeros: Enter through the Standard Queue. Follow directional signs to designated load area.
- American Adventure: See a host or hostess for access to second floor
- Impressions de France: Enter through LEFT side of entrance hallway
Studio
- Great Movie Ride: Enter through the Standard queue. A host will provide directions in the pre-show area
- Studio Backlot Tour: Enter through the standard queue and stay to the RIGHT
- Fantasmic: Enter through the standard queue and stay to the RIGHT
Animal Kingdom
- Wildlife Express Train: Proceed through standard queue. A host will direct boarding
- The Boneyard: Enter through the designated access gate
Everything other than these attractions I have listed say to enter through the mainstream or standby queue.
The maps are very easy to read (although the type is small) and I recommend you get one for each park. The access information is listed right on the map with all the other information. There are icons that show which attractions you can stay right in the wheelchair for the whole attraction, which you need to transfer to a ride car.
If the double stroller is 30 inches or less in width and less than 48 inches in length, it should fit in most lines. You would need a Guest Assistance Card or sticker to use a stroller as a wheelchair.
If you follow the link in my signature to the disABILITIES FAQs thread, one post in that thread is about bus transportation and should be able to answer all your bus questions.