Plumbing Question - Hose bibs and branching off lines

[TwinbrookNine]

It has nothing to do with branching. There is no reason they should be that different in PSI except for the difference in valves at the hose bibs. They sell "water conserving" things these days (like shower heads, and God knows what else), and the low pressure could well be due to one or two of those hose bib valves. The ID of different valve types at an open position can vary a lot. The ID of that hole in the stem of a valve is not a standard thing.

[Electrician4you]

You may have a hose bib that does not open fully or its restricted in some way

[threecats407]

Everything I see looks like Joe Handyman work including a load of pvc joints that will be failing at some point.