more answers than expected!!
He does a lot of mountain biking, bouncing off trees and such. She's more of a car person, which is why I'm thinking e-bikes will be a better intro for her. I'm looking at a day trip--they are staying with me in North E'burg for a few days.
The only place I've seen (personally in person) a Highland Coo locally is at a garden centre just inside the bypass, but I can never remember where it is.
They just really want to see a Highland Coo, and as I'm not sure where else in Scotland they plan to go, I thought I'd try to fit one in on this day outing.
Roslin to Portobello could be doable--that's a fairly flat and off-road 30 minutes from me.
Thank you all so much, I'll have a look through these suggestions, and then distill into a mini-guide for them.