Some compressors are 10 Bar, 140+psi.
Thought 10 bar was 150psi?
Coming from the Instrument background where 3-15 psi = 20-100 kpa and 1 bar is roughly 100 kpa (without getting all technical)
Only know those figures as I may have been the reason for safety overflows on a U Tube manometer
I feel that your idea of multiple compressors may actually work well for the purpose.
But id suggest you have it set up with 1 way valves to stop any potential back feeds.
Also if you can maybe set it up to go into a header tank.
So 2 compressors feed in via the 1 way valves (pressure regulated would also be ideal) to the header tank.
Another consideration is the current draw with having 2 compressors. If you have 2 power circuits may want to run them on seperate ones as there is the chance an inrush may trip the circuit breaker if on the same circuit.
As for the 3 phase off the VFD. I have done a similar set up before but on a table saw. Just had to be mindful of how heavily it was loaded and setting up ramp times etc to not pull too much current upfront.
And also check for any leaks you may currently have with soapy water.
You may find something is actually leaking which can cause a bit of air loss.