Trying to decide what would be the best way to send wireless signal outside from one building to another parallel outbuilding through windows facing each other.

Spacing is around 20-25 feet apart and I need to hard wire 3 PC's together on a switch (to share information) in the outbuilding and possibly wireless with another PC in the main building where the modem and router are located.

I was looking at the Deco S4 (3 unit home mesh Wifi) system and thought I could put the second unit in the main building window and the third unit in the other building window to relay the signal but will I be able to attach a small switch to the very end of the third unit (in the outbuilding) and be able to obtain decent speeds and connectivity with all 3 or 4 PC's? 

Other posts only show a switch in between the chain units and don't give any indication of being able to share information via the switch or internet connection speeds. Thanks for any information you can provide.