I’m not sure if you can use two tobii sensors together (at least the x2-30s). I know you cannot use multiple eyex sensors together, but there are several request for this functionality. I assume this is for a multiple monitor usage?
As for fatigue detection, there is a good bit of research on blink rate, eye closure rate (blink duration), and a metric referred to as PERCLOS (percentage of eye closure) that have been shown to correlate with fatigue detection. I’ve not used the analytics SDK, but i’m sure you can pull this metrics out of the data with the provided tools.