In order to do that you just have to make sure that the padlock icon on bottom right-hand corner of each chart is locked. After that double-click on a currency  in "Streaming quotes" tab of "Quotes and Analytics" window and the charts you have "locked" will change their currency simultaneously. 
If you want that the charts to reload quicker, then make sure that each of them has less chart history enabled. Do that from "Securities" section on top left corner of the screen (red/green arrows icon).