B737-300 Brake System question

[Tee Emm]

In the 737-300 simulator with engines off, APU powering both busses and both electric hydraulic pump switches off. Brake pressure needle indicating 1000 psi. The "A" hydraulic System electric pump was turned on in the expectation it would increase the indicated brake pressure to nominal 3000 psi. But it didn't and the brake pressure stayed at 1000 psi.
However, after turning off the A system electric pump and activating the B System electric pump the brake pressure increased OK.
The FCOM states the alternate brake system is pressurised from System A and that if hydraulic system B is low or fails, hydraulic system A automatically supplies pressure to the alternate brake system.

So - here is my question: With engine driven pumps inoperative (on ground engines off) and B electric hydraulic pump off, would it be correct to assume selection of the A system electric hydraulic pump switch to on would activate the alternate brake system to pressurise the brake pressure gauge to 3000 psi? Because it certainly doesn't in the simulator.

Additional question: Scene: engine or APU Fire Warning on ground aircraft stationary or taxiing, or: Evacuation.

FCTM page 8.9 has sub-heading "Recommended Technique for an In-Flight Engine Shutdown" and in this case the PF directs the PM to move the start lever to cut off and also to pull the engine fire switch. However if the problem above occurs on the ground, the FCTM is unclear if the captain handles the procedure himself ie cuts the start lever and fires the appropriate bottle -or - is the procedure the same as In Flight (PM does the work while the captain is only responsible for closing the thrust lever?

I never ceased to be amazed over the years how a simple closing down of an engine on fire in the air, or on the ground, is the subject of so many personal opinions in terms of who is responsible for what lever and who says what. Having flown for several 737 operators it seems each one has a different procedure including one whose policy is that the captain always closes down the engine and fires the bottle (airborne or on ground) while the F/O monitors his actions. Boeing skirts the subject and seemingly prefers to leave it to the operator to provide it's own policy. Friendly constructive comments always appreciated. Thanks.