Many of us have aging guests invited to our wedding or guests that have special needs that if we accommodate them, will enhance their time with you.
While having a microphone for speeches is usually a given, make sure that for your ceremony there is a microphone, even if you are in a small space or with a few people. Those with hearing difficulties, tire easily from trying to hear what is being said. Also if you are outdoors, sound drops at about 10 feet. What you are saying is important, so have that mic available. You may also want to have them seated close to the front. If any of your guests are deaf, contacting your local CNIB will put you in touch with interpreters who can use ASL to better include your guest.
For those who use wheelchairs or walkers, perhaps you may need to have a ramp so they can sit where everyone else is sitting. Motion Specialties and Duramed in London, but rent ramps at a reasonable cost. Once your guest is in the room or area where the ceremony will take place make sure there is a place for them, INSIDE the same section, and with enough room around them, where others are seated. People especially those in wheelchairs, do not want to be sitting in the aisle, they want to be like everyone else!
If your loved one has dementia and may need to excuse themselves in the middle of the ceremony, perhaps hiring a companion that can take care of their varied needs, while not effecting family members, would be a good idea.