Carbonfiberboy 

Reading this thread, a two wheel tandem seems to be the obvious solution. There is a way to find out. Either find a local tandem team (best) or visit a bike shop which sells tandems. What you want to do is:
1) You go out as stoker with an experienced tandem captain.
2) You go out as captain with an experienced stoker or captain, and for more than just a few minutes. .
3) You try it with your wife as stoker, first time in an almost empty parking lot.

The trick for the stoker is to not influence the balance of the bike, no anticipating a turn and leaning for instance. Stoker remains absolutely still, just sitting there. In my experience, the stoker should always be clipped in, either clipless shoes and pedals or toe clips. That way her feet can't come off the moving pedals and whang her ankles, guaranteed to give one a negative opinion of tandems. It doesn't matter so much what pedals the captain uses.

The trick for the captain is to learn the Proper Method (google) and just ride the bike. A tandem is much more stable than a single.
https://gtgtandems.com/tech/propmethod.html

We started tandem riding in 2007, when our team age was 117. We're still at it. My wife loves it.