The 2 remote switches may be the starter cut-off switches. Quick test is to turn both remote switches and the DC selector switch off and try both engine starters. Turn one one and see if only one engine cranks or if they both do.
If they both crank with 1 switch on, switch logic may be:
Switch 1 on, both starters powered by battery 1
Switch 2 on, both starters powered by battery 2
Both switches on, both starters powered by both batteries, the batteries are connected together at the switches.
To (maybe) split the banks, turn remote switch 1 on and DC selector switch to position 2. This may turn battery 1 into the starting bank and battery 2 into the house bank. Each alternator would charge its respective battery.