Find out what is used on tandems, all sorts of tandems, Santana, Burley, Miyata, Counterpoint, Rotator Recumbent, . . . The "theoretical" biker the magazines like to use is 150 pounds so two of them is 300 lbs. A set of tandem hubs sounds like they would be just right for you. But remember: "You can get anything strong, light, cheap; any two of them but not all three." A set of, say, Phil Wood hubs could be strong and light but not cheap. A set of hubs from a Walmart bike would be cheap, heavy, and weak. Saving a few ounces is silly at your weight so I recommend strong and inexpensive.