How to wire two light switches, two lights, and one duct exhaust fan so lights work independently but fan works on either switch?
This is very similar to a question I answered here. Use DPST switches, such as those intended for water heaters. 

Note that this solution already contemplates the issue of the ligths/fan not all being on the same circuit.  

It does not consider having the switches some distance apart. No matter; one of them will be a switch loop.