Question #1: No idea on GPM @ 3000 rpm between 6 and 12 is all I got on that...
Question #2: Just assume that aircraft hydraulic utility system ,when No 1 EDP pressure is 3000 psi and No.2 EDP pump pressure 3100 psi how the pressure act passes thru passage of single pipe after isolation check valves ?
The 3000 PSI pump will be at zero flow because the pump compensator (set at 3000) is satisfied with the pressure. The isolation check valve for this pump will be closed due to the 3100PSI being applied to the check valve preventing it from opening.
The 3100 PSI output pump (compensator is set incorrectly) will displace fluid to maintain 3100 PSI, it's isolation check valve will be open and the system pressure gauges will read 3100.
As hydraulics are used the pressure will drop and the 3000 PSI pump will be allowed to help out but only until the 3100 PSI pump builds its pressure back to 3100, then the 3000 pump will again go to zero flow condition.