1991 Toyota Camry BRAKE BLEEDING

Did you replace master cylinder because it was leaking? Pedal pressure changed and or had to be pumped to stop car?

It is odd that the rear passengerr and driver front brakes aren't working.
The reason I say that is becasue when you bleed a system you start at the farthest brake from the master cylindr and work towards the closest to the master cylinder. The rear passenger is farthest and the driver front is closest.

Did the master cylinder come with a bench bleed kit?
Aside from checking for brake caliper or slave cylinder lleaks, try the following;

General procedure bleeding brakes.

Get some clear hose that will fit on bleed screw and stay on fitting snug enough to keep air oout and fluid in. Usually you can find this at local hardware store. Put some axle grease on threads of bleed screw t avoid any air making it back into line. Get a bottle to capture brake fluiid.
Attach hose to the bleed screw on the rear passenger side, run the hose where you can see the fluid as it runs through hose and in a position that brings it at least a few inches above the caliper/slave cylinder you are bleeding. Place the other end of the hose in the cpature bottle till it is in the bottom of the bottle. Have assistant pump brake and hold brake pedal to floor after a few pumps. Release bleed screw and then tighten it while the assistant holds pedal to the floor. Repeat until there is at least more fluid than air coming out. At this point the assiitant can pump brakes without losening and tightening the bleed screw. This is because air is sealed out by hose and grease on bleed screw. There should be enough fluid in capture bottle that the hose is well under the level of the fluid expelled from system. Continue until there is only a few air pockets coming through the line. Then pump the pedal and hold it, tighten bleedd screw, release pedal, pump several times and hold to floor, loosen screw and tighten it while pedal is held to flor. Only release the pedal when bleed screw is tight. Eventually, you will be able to see that the fluid in the hose does not have any air in it and that caliper/cylinder is bled free from air. KEEP THE MASTER CYLINDER FULL OF FLUID AT ALL TIMES OR IT WILL SUCK AIR INTO SYSTEM. If the capture bottle needs to be emptied, (keep enough in the bottom to keep hose immersed in fluid), hold pedal to floor and then take bottle, leaving the end attached to the bleed screw in place, and remove some fluid.
The next brake to bleed is the rear driver side, then front passenger side and finally the front driver side.
If there is still an issue, then further diagnosis is needed.
Let me know how it goes.
Then go back to pumping pedal and holding it to floow, tighten

Check the oil pressure with a mechanical gauge, if normal replace the oil pressure switch. If abnormal could mean oil pump and engine bearing. Are you talking about no fluid coming out if so recheck the proportioning valve and the master cylinder

I think the proportioning valve is a load sensing type.
P- valves keep the front and rear brakes at the proper pressure as to stop the car as fast as possible without the rear brakes locking up before the fronts.
So, if the system has not been flushed regulalrly, there is a good chance it needs to be replaced. However I still find it odd that the font driver won't bleed since it is closest.