I can tell you how a battery isolation module is supposed to work…
Case 1, charging voltage is detected from either the engine's alternator, the generator, or shore power, house and chassis batteries are connected to allow all batteries to charge. Note that this pretty much requires that all batteries be wet-cell, or all batteries be AGM, or else one battery type will get the wrong charging sequence…
Case 2, no charging voltage is detected, but a drain is detected on either the house side or the chassis side, the battery isolation module disconnects the systems to prevent the other system being discharged along with the one that is discharging.
Engineering: Finding complex solutions to simple problems you didn't even know you had.