https://help.guildwars2.com/hc/en-us/articles/360013658134-Policy-Dual-or-Multi-Boxing - Provided its one person, three computers and three accounts running simultaneously there is no EULA break. Its only an issue if they are macro'd or controlled via one controller, I.E three characters executing the same skills at the same time and moving around the world at the same time. Report non-the-less and let ANET do the investigation which I'm sure they do... but just make sure you can see the actual botting-like behavior and not just multi accounts being used at a spot to farm something.