Did u check the airerators on each faucet ? do that first---------- OLD GALVANIZED WILL MORE THAN LIKELY NEED REPLACED. I T WOULD BE COST EFFECYTIVE FOR U TO BUY A "PEXS" TOOL , PIPE AND FITTINGS , AND START REPLACING IT UR SELF, ANY ONE CAN DO IT !
I JUST REPLACE MINE AS EACH LINE GOES BAD, SOME NEVER WILL.