So ive got city water and it comes into the house with 1/2 pipe from the street. The house has always had pressure problems so a couple of months ago I redid all the plumbing in the basement and 1st floor with pex and a nice pex manifold. The pressure is good (not great) when im only using one thing. The second I turn on a second fixture the water practically comes to a drizzle. I bought a pressure gauge to test the pressure at the outside spigot. Regardless of how many fixtures are on it stays in the 90-100 psi range.(im not totally convinced im getting an accurate reading from it) I want to install a pressure booster pump to help keep the pressure when multiple fixtures are used. But the pump website is saying the highest my pressure can be is around 20 for the pressure switch to work correctly. Can someone guide me in the right direction?

Ok so I'm building a house and im up 200 ft from the street where my water main is located. I have about a thousand feet of 2" water line to the house and the county pressure at the street is 90 psi. When I turned on the main it put 120 gallons of water in the pipe unfortunately it was not enough to get to the top of the hill. So in the basement I have a 1 hp jet pump and a pressure tank set up. I am having trouble filling the rest of the water line and cannot seem to get the pump to prime. I fill everything and it builds pressure for a second and then drops off. When I open the pump it is empty. Air in the line? Is the pump under sized? I put a valve in line and ran a hose from a submersible pump in my pond in hopes that the pressure would break up the air in the line but it only builds to about 10 psi. I tried using it to help prime the jet pump and the pressure will build to about 40 psi but as soon as I close the valve the pump sputters and loses pressure. I'm not sure how far I'm trying to pull the water it should be at the top of the hill and only like 30 ft from the house. I'm not pulling vertical mor horizontal. Any help would be great. Thanks.