Hi A.,
I suggest checking out the Disney on property hotels as well. There are some special deals going on right now. They also provide free transportation from the airport via the Disney Express which will save you quite a bit of money. Disney has 3 classes of hotels including value resorts which include POP Century (my daughter interned there and lots of families stay there) as well as the ALL STAR Sports and Music venues. Check on these because they all provide free transportation to all the parks. If you drive a car and are not staying on Disney property, then parking is $11 or $12 a day
Some of the off-property Disney tied in hotels in Lake Buena Vista also provide free bus transportation to the parks. Check these out -I think they are part of the Disney Good Neighbor program. If you check any of the travel websites, and google Lake Buena Vista, you will get a big list of available properties.
Also with 9 people you might want to see if you could find a condo so you could have cooking facilities. I googled Lake Buena Vista condos and found one Lake Buena Vista Resort Spa that is 2 miles from park, provides free transportation, and has 2-3-4 bedroom condos. I have never stayed there so I can't give you personal experience, but there were also other condos listed.
Good luck and have a wonderful time. September is kind of off season in Orlando (since school vacations are over) so there should be some great deals. Some might not come out til later.