I am designing a refit electrical system around the design for a catamaran shown at link below but with only one 100A alternator on each engine.
The alternators with external regulator would be connected to an Argofet 200/3 battery isolator then to 3 battery banks (1)House 600ah L, (2)Critical systems200ah L and (3)Enginex2 with 100ah AGM batteries charged off the alternators external regulator set for AGM and the lithiums seperated by an Argofet 100/2 and charged by Orion DC DC smart chargers set for lithium.
Link to schematic the above would replace engine Alternators in schematic to protect alternators in case of lithium shut down.
A simple diagram of your proposed install would clarify what you were planning rather than trying to decipher a description.
I do not understand the need for the 200/3 Argofet. Each alternator charges its AGM engine battery. You then input from each engine battery into a DC to DC charger. The DC to DC chargers output to the Argofet 100/2 to then charge the lithium banks.