The best option would be an Ethernet switch, they are cheap and reliable. Do note that you'd need 9 connections, one in and eight out, making a 16 connection one your best bet. Do search Sonos support for "incompatible hardware" and don't get the wrong one.

You will probably end up getting a gigabit switch, no sense in getting a slower one. 

You could put the switch central to the speakers and run a single Ethernet line to it, that could save you a lot of wire.

Amp would be of little use  a Port would give you an easy to access input to feed local music into. Not good for PA use due to the Sonos processing delay.

Additionally if I wanted to input music to the system using wired connection ie AUX what would I need and how would I achieve this?

The Ethernet adaptor also accepts line-In. If it is inconvenient to wire the Aux source to an adapter, you can use the Line-In on another device, such as PORT or FIVE.

Just to make sure that I am not misunderstanding anything I drew out a diagram. 
Am I understanding the set up correctly? Are these two options viable?

Thank You all for the help

@dlejund just double checking this setup will be used for pre-recorded music etc and not be used for ‘live’ music feeds, DJ or PA system, as there will be a delay?

You will also need router connected to switch in your setup (2).

Setup one is good.

Setup two, no. Do as setup one  but with the Port connected along with the speakers to the switch