If his shower turns off when someone flushes a toilet, he has some serious plumbing-piping issues. More pressure will help but not solve that. Crank up the pressure to a 50-70 shut off and see if it helps. If it blows out the old pipes, that's the inspiration to run the right size pipes to the shower and toilets.
I know Murphys pretty well. A once small and quiet, innocent sleepy Sierra mountain gold mining town turned into a over priced, gentrified, wine region destination. If you do find a competent technician [not really a plumber and not an electrician, but a combination of several trades and skills] you will pay dearly in that area. All the good and honest well people are in boot hill.