Re: Plumbing Multiple Shower Heads?
Yes, the reason for the loop is that the first emitter in the series would have more pressure than the next, and the very last would have almost no pressure. The loop equalizes the pressure so it's always exactly the same between the two heads.
I can't think of how a third shower head would improve matters.
Your temp/mixing valve must be flow-rated for multiple heads. IOW, you don't want a water-saver mixing valve.
Remove not the ancient landmark, which your fathers have set.