We often have multiple charging sources. If we have 2 inverters we have two sources. They will not supply a greater charging voltage just because 2 are being used.

What concerns me is why the need to keep a charger on chassis batteries. That suggests a load on the batteries (or failing batteries) when the bus is stored. I can literally allow my coach (both that I have had) to sit for as much as 3 months and the chassis batteries will still be at 24.5 volts or so, more than enough to start the caoch.

I would seek the reason a charger is needed.