Salt deposits in health faucets and shower

Larger supply piping and a "parallel" (as opposed to "series") manifold arrangement will help, but you need to realize that there is only so much you can do. You are limited by your home's water supply pressure and size.

Probably the easiest thing to do is use low flow "water saving" shower heads/nozzles.

If you want to do more, check the size of your: water meter, water meter union, and main water line. Increase the size of all if possible. Also, check to see if your main water supply has a pressure regulator installed. Check your static (no-flow) pressure downstream of the regulator to determine if you can raise the regulated pressure (check your city bldg. office for max allowable pressure). Older homes with steel water piping often suffer from low gpm/lpm flow rates, consider a complete re-pipe if this is the case.

Acid. Vinegar, Citric (aka sour salt), CLR, Barkeepers friend, phosphoric, etc. Keep applying (and re-applying) it, and see if perhaps you can get dry citric acid or barkeepers friend mixed to a "paste" or "slurry" form that might cling to the problem area - or fill the trap with acid and use sections of rope or rags (secured against going down the drain) to act as wicks.

You might also want to install a softener if your water is so hard it's growing stalactites. Yeesh.