If my understanding of stone is correct, you are a big one! I'm going to guess that most bike parts will be adequate. The reason I think that is because, with a few exceptions, tandem bicycle parts are similar to similar to those on single bikes.
I think that I'd avoid suspension. There are fully suspended tandem bicycles so I know there are parts available that will be adequate for your use, but I don't know enough about them to advise you what to look for and what to avoid.
Wheels are a common weak point for even average size riders. For you I'd recommend 26 inch wheels with double wall rims and at least 36 spokes. If you can find something with LX or better hubs and Rhynolite rims, that would be perfect.