Because they are basically in the same location, the problem obviously is in or near that location. The simple (and first thing a plumber will check) is the strainers on the faucets and crud inthe valve at the toilet.
An expansion tank will not do a thing for the problem. They are used as "overpressure" protection on a sealed system (well or house with a one=3Dway valve on city water). They also cure water hammer if they are near the source of the 'hammer'.
Harry K