Hi,
Welcome to the forum.
I am as tall as you, but with a 33" standover height wearing shoes. I ride a straight handlebar 560L size Thorn bike which is the equivalent size to the Sherpa 560xl and find it fits fine. If I had another 3' of inside leg then the saddle and handlebars would need to be quite a lot higher on this size of frame.
I would suggest that Thorn have got it about right for you with the larger frame.
The really good thing is that Thorn will change it for you if you are not happy with the size provided, so there is no risk in taking their advice for starters.
Whatever size you end up with, I hope both you and your wife enjoy riding your new bikes.