As of now, syncing tootTips across multiple charts isn’t possible, out of the box. However, we are considering it for the future versions. For now we will create a work-around and get back to you at the earliest.
You can sync toolTips across charts by getting the pixel co-ordinates from the first chart & then triggering an event in second chart and so on. convertValueToPixel() and convertPixelToValue() methods can be used to getting the pixel co-ordinates & corresponding values. Here is a jsfiddle for the same. Please note that there may be a slight variation in x-value as pixel co-ordinates are used.