Hi Theresa!
How wonderful that you are planning a trip! September is an excellent choice for your vacation. After Labor Day, the crowds thin out significantly, which should help you all enjoy your time in the parks even more. You should also be happy to know that all of the resorts at Disney World have accessible rooms. Specific features vary by resort, but an excellent resource/place to start planning is
HERE, which is the link to the Disney World Guests with Disabilities site. The site contains an additional link to a number of Frequently Asked Questions, helpful phone numbers and other information frequently requested by guests with special needs. In addition, should anyone in your party have dietary concerns, allergies, etc. the site contains information that should facilitate your dining experiences.
If you'd like to speak to someone in person regarding your specific questions, concerns or the needs of those who will be travelling with you, please feel free to call 407-939-7807.
I would ensure that one of your first stops in the parks is to visit the Guest Relations area, where you can obtain "Guest Assistance Cards" for those in your party. These cards will assist Cast Members operating the rides help direct you to the appropriate, accessible entrance for your party.
I hope you all have a magical trip!