It's generally a very long and exhausting day. It can be blazing hot too. The oath and visit after to see the transformation is probably the biggest event. If they have trouble getting around, I would pick that part of the day. I believe if they have a handicap placard you can park on the yard. I would imagine on I Day this would even be full very early, so wouldn't count on that later in the day. I am sure the I Day packet addresses all this. The buses that run from the stadium drop off at Alumni Hall if I remember correctly. The walk from there to T Court isn't bad, but probably could be for someone who has trouble moving. Also there is only so much room to see in T Court. So possibly being a camp chair for the person who needs assistance.
There are lots of previous thread about I Day on here, I would check those out. It's a long exhausting hot day for everyone. There is tons of walking. So depending on what you and your spouse want to do, such as the Mid Store and picnic and things that would be an issue for someone who struggles getting around.