Question From a Really Big Guy Maybe You Can Answer

I like the seat riser idea. Although some of us (not naming names) gain enough winter weight that there's a possibility one's tummy might get in the way of a steering wheel.

There are all sorts of great modifications and assistive devices, tricks and tips. I'm sure the OP can find something he and his wife like that will work well for them.

The first step (bad pun totally intended) is getting them out to see some coaches!