indoor positioning network

So i recently bought 4 xbees s2c (3 of them attached to an arduino uno board),
I want to have 3 fixed xbee nodes to do triangulation on the 4th mobile xbee to determine its position using RSSI in a small indoor room (approx 10mx4m).

I am a bit confused on the CE coordinator/end device mode on XCTU, I dont know which ones to have as a router/ coordinator or end device?
Also is there any way to use the range test on XCTU for more than 2 xbees?