You build stuff and good with your hands, right? I bet you could build something awesome to house a couple of guineas and a bun! I honestly don't know whether they'd be okay together... gut instinct says probably be fine, but would still get two guineas so they have each other for company, even if they live together with the rabbit. But again, haven't kept them in decades, I'm not the one to advise really!
They really appreciate some outside time too, a moveable run you can put them so they can eat grass (so long as you don't use weedkiller or anything) and get some fresh air! But supervised because of cats and foxes. I'd just put them in the outside run for some outdoor time while I or someone else was in the garden to keep an eye on them.