Explained volume vs pressure, the pipe size for the main water line from the meter to the home is 3/4 rather than 1in, so therefore there is a volume issue on how many bathrooms there are in the house (3.5). In order to have more flow, you’ll need to upgrade the main service line to 1 in rather than 3/4. That would be the fix for the volume. As for the water pressure, it is normal, it is at 65psi, the pressure only drops 5 psi when a toilet is flushed, when 3 or more fixtures are being ran the pressure drops to 50 psi. There isn’t enough volume of water to keep up with the demand.
