I decided to err on the side of caution and go with the tandem tow dolly for now. Plus I got it for a great price. I'll be sure to keep it under the GCWR and check the axles independently. The bikes are both honda shadows, one 750, and one 600. I forget the exact wet weights, but they're around 504, and 420 lbs respectively. The tow dolly has a capacity of 1200lbs cargo + 5000 lbs car on an 8000lb axle. Now I just have to find a little fwd toad that the wife likes
Thanks again for your input everyone. I'll update once we've gone out for a trip or two.