For the convection and stoker motor outputs this should be okay, so long as the combined current draw is less than the ratings on the two outputs. Run Y-splitters for each output (parallel circuits, not series). This is basically no different than we do on a dual burner furnace, except that the distances are less and we have a special version of the software and hardware to allow for changing between one and two burner operation via a parameter setting. In your case you will simply unplug one of the stoves if you only want to burn one of them.
I would not recommend running a y-splitter for the convection blower output. On units with two matched motors and short cable runs we can run the y-splitter for dual speed control on convection motors, but for your situation I think it would be a problem. Even if the total current draw is under limit, the distances involved and differences between the motors on a speed controlled output will likely result in the circuit ending up stuck full open, regardless of the speed being commanded, until the control commands to shut the output off.
1) With the dual load on the circuit, if one of the stokers gets jammed, even slightly, you will be more likely blow the stoker circuit than if you were just running one stoker.
2) Even if you are under current limits for the circuits, the control module will likely get pretty warm so make sure it isn't enclosed or contained in anything. If possible have some air moving around it to help in cooling it.
When you first try running both, keep an eye on the control module and check the case temperature around the two rivets on the cover. If they get hot to the touch, you'll need to run a fan blowing on the control unit or discontinue running both at the same time off the same control module.