I took one of the Overlord full-day tours in 2017. I wish I had a better memory for how things played out. We would stop at a point where the van could park then walk to the point of interest. The group members didn't walk at the same pace and some paused to take pictures, so we sort of straggled over to the place we were heading for. The driver/guide sometimes gave part of his explanation while we were very near the van and part of it later. Some of the walks were very short; some were longer. At least one was over bare ground rather than paved paths and did involve a good bit of walking away from the van. However, this is not at all like a 2-hour walking tour you might take in a city. You are being driven from point to point and do not spend a great deal of time at any location except for the lunch break at St-Mere-Eglise, and most of the time there you are on your own to grab something to eat and visit the Airborne Museum.
Incidentally, I strongly suggest that you just take something with you so you can use most of the time to see the Airborne Museum. Even if you just buy a carry-out sandwich (the driver will point out a place where you can do that), that will take 5-10 minutes you will later wish you could have in the museum. You are not allowed to eat in the van.
I don't think the tour will be too difficult for your husband, but it's possible that he may occasionally miss out on part of the guide's explanation if he is slow to arrive at the target point.
