I can only use one faucet at a time. If the laundry is running, you can't do dishes. If you flush the toilet, you can barely wash your hands. If one shower is going, the other one waits. What can I do to make my water pressure consistent and constant?

City water or are you on a well? Just as bad with cold as with hot?

City water. It is just as bad with cold as hot but it does take a long time for the hot to get to where it is suppose to be but I think that may be a separate issue.

Do you know if you have a pressure reducing valve back by he meter? Watts Water Pressure Reducing Valve Series 25AUB-Z3 3/4" (0069717) at Remodelr.com

I have no idea

That's why I gave you a picture of one. If you have one it would be mounted on your side of the metered supply line coming in from the city. Likely right after your main shut off.