Did you figure this out yet?

I would turn off both switches and try to start engine.  I would expect no start.

I would then try each switch individually and see what happens.  This will give you a sense of what each switch controls.

I believe there is a battery isolator that separates the batteries. The engine alternator goes to the isolator and then splits to the separate battery banks.  The batteries should not back feed through the isolator.

Hope this helps.  Safe travels