I am not aware of any Downtown Disney hotels that have full kitchens. Have you considered hotels that are not in Downtown Disney? There are many options close to Disney World.
What do you mean by a kitchen? If you mean a microwave and refridgerator, there are lots of options, including some Downtown Disney hotels. If you want a full kitchen, the options are more limited. There are a few full service hotels that have full kitchens and there are always condo rentals (I prefer the maid service myself).
You might checkout Holiday Inn Family Suites. This is a fairly new hotel very close to Disney property (about 5 minutes to Epcot and to Downtown Disney).
They have suites with a full kitchen and 1 bedroom (residential suites), and other suites with 2 bedrooms and a mini kitchen (microwave and refridgerator). Each suite also has a sofa bed in the living room. You could connect the residential suite with the 2 bedroom or could connect 2 of the 2 bedroom suites if the full kitchen was not necessary.
The hotel is targeted to families, but they have a courtyard that is
more adult oriented that you could request. Bathrooms are large, bright and modern. My only complaint is that drawer space for clothes is somewhat limited (only 3 drawers in each bedroom). This could be a bit of a problem with 8 people.
If the inlaws are over 50, the hotel has great "senior saver" rates. There is also a fairly good hot buffet breakfast that is free for everyone in the room.
The web site is
www.hifamilysuites.com. Good luck finding a place.