question

The issue would be how does the limiter react when the multiplus says the batteries are full and the grid is off so it cant export if it has no other option, and it wants to reduce the solar input to nothing. Normally the multiplus does this by increasing the frequency from 50hz to say 51.5hz and the grid tie then reduce there output in 10% or so increments from 50.5 to 51.5 by 0.01 steps or 10% per 0.01 hz change. (this is just a ruff idea of what normally happens).

so does the limiting device reduce its output from 5Kw to say zero if required as the hz is changed.

normally the multiplus is being used as a micro grid that controls thats Grids frequency when there is no grid or generator, now having such a large array on the AC out side might override the ability for the multi plus to control the frequency correctly as well

so I would say that its NOT recommended in any way shape or form , and to do it may damage the inverter. or the batteries as they would get overcharged or the AC voltage could go sky high as well.

Put the extra PV inverters on the grid side of the inverter. would be the best place for them

This will not work. 4:1 is really high. The peak that will come through before the limiter is able to responded would be 20kw and that will instantly trip the multiplus, possibly damage it.

A 2:1 might work but is still not recommended at all.

On an off grid system like this you need your hybrid inverters to be able to cover the loads fully.

If you 15kva is enough for your loads then you could install 3 multiplus-ii and 2 or 3 AC-PV inverters.
Add the rest of the solar to Victron RS 450/100 or 200 MPPTS.