I have a single switch that controls two lights, that I would like to split onto their own switches. There are two sets of wires coming in and one going out in the gang. I can put in a 2-gang, but I can't quite work out the wiring for two switches?

Lets see if I can help here.  From what Im reading you have three sets of wires in that box. The question now is did the Electrician run both wires from the lights back to the box or only one and then a set between both lights.  You can test this by finding power in and then touching it to the other wires, one at a time and see what happens but make sure both lights work. Im guessing there is only one switch leg in that box and other is power in and power back out to something else. If this latter is this case, contact me and Ill help you fix this