The 1/125 Revell VII-B is also twin prop but as I recall the builder used a single prop mounted lower than the twin props on the original model. He just made the thing work and was not overly concerned with scale issues. At the time the build article was written, 10+ years ago, the ability to micro RC was limited compared to nowadays.

For simplicity's sake, I too would probably forego the complexity of attempting a twin motor or two propeller/one motor & gearbox setup in favor of one propeller.

If you're making the Lionfish a static diver, I'm very interested in reading more.