You should be able to feed both inverters off your battery bank, but you cannot combine the inverter outputs. You can install 2 separate sub panels and feed each panel from a separate inverter.
I recently installed a new Heart Interface 2000 watt inverter that had one 120 AC line in and two 120 AC lines out. I called Heart Interface Tech Support and asked if I could combine the two 120 AC out lines. they said no, I had to feed two separate sub panels (this inverter had 2 AC out circuit breakers on the front of it).
Of course, you realize that if you run both inverters off your present battery bank, you will run your batteries down quicker? Jack
How did you handle the neutral ground bonding in this situation?