Maybe you don’t need that big batteries… Basically a double-conversion UPS can be assembled from Victron parts.
Charge batteries with 3x Quattro from grid or generator, which should provide a pretty stable load for the generator. There’s a lot of tweaking options in the config for dealing with generators. This is the input stage and only provides power for the DC bus and batteries.
Then convert back to AC using another 3x MultiPlus (or Quattros). Power goes via DC bus with battery buffer, so that’s not efficient at all, but you’re fully in control of your output power quality then and your generator is effective decoupled from your load spikes.
Sounds like your PV is AC-coupled, so that can just go on output.
Essentially you’re running a microgrid from solar and battery, but with additional mains / generator battery chargers.
You could also bypass the chargers and use the grid directly into your output stage Multiplus / Quattro set, but that won’t cleanup the power. Could work well enough 80% of the time and when you’re fed up, you switch to double-conversion for the week?
@JacoDeJongh has experience with some pretty big systems, so should be able to design something good.
These things exist as off-the-shelf products too under traditional UPS labels.
Double-conversion vs Line-interactive: Double Conversion UPS – Benefits & Comparison | Mitsubishi Electric
Edit: This is massive though: Does anyone have a grid-tie system with no storage? - #10 by Scubadude
Victron tops out at 180kVA for 3-phase 
… Maybe do 5x, one per 100kW SolarEdge 
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