Your use of the previous MPPT charger, as a voltage converter/battery charger form the 12v systems is very clever, but I don't know if this will require you to keep at least one AGM battery in place (to power the MPPT electronics 24x7). Aside from powering the "old" MPPT electronics and slightly stabilizing the output as a filter, it just sits there as a 'pass-through' device on the way to the terminals of the 12v panel.
I have three wiring comments and one MPP Voltage concern: First (WRT wiring), your "50A" generator is going to need much larger wire on the 120-VAC side, into the MPPs. If you fuse the circuit at 60A, then your wire size needs to be AWG-6 or even larger. You can use either a fuse or a Circuit Breaker, but the safety limiting device must be smaller than the wire's capability.
The same applies to the shore power 120-VAC limiting device: Although they will always have an AFCI/GFCI at the "shore" plugin, your wires and cords need to handle everything which their plug is willing to dish out. (If you size for 30A, then you need AWG-10 or larger).
My third AC wiring concern is with your "Downstream", where you use AWG-8 (40 amps max) but provide a 150A breaker/fuse from each MPP. The MPP's, if rated at 3Kw continuous and 6Kw maximum, are officially incapable of exceeding 60A in any situation (that's 7200 watts). I would want to increase the wire size of these "mains" into the port and starboard mini-boxes to at least AWG-6, and I'd cut the fuse/circuit breaker rating down to 60A.
Second, I'm a bit concerned about running Zone-1 into the MPP at a voltage which is so close to the MPP's maximum rating. I prefer to design with V(oc) no higher than 80% of the rated limit on the MPP's 'Solar Input' Voltage.
Your plan otherwise looks great to me, carefully designed and beautifully drawn for consideration by members of this forum.