Batteries, isolators and mixing

It's not a wake boat but I know someone here can help.

I have a boat with 4 batteries; House, Engine 1, Engine 2, and Genset. I end up changing out the wet cell batteries approx every 4 years but I'm not sure if it's worth spending $90 on wetcells or upgrading to AGM's at $265 each. I'm thinking of installing an AGM for the house, as this is the only battery that gets drained, and wet cells for the engine and genset. MY question, can this be done?

The boat has two isolators and an onboard charger that runs on shore power or the genset. The two engines have alternators but not the genset. There is a parallel switch for the engine starting batteries although I don't know what it parallels with. Each component has it own cut-off switch. Batteries are all group 31 with approx 1100CCA.

Ironically, the batteries all seem to die within months of each other.