You know, I think a timeline of The Real Ghostbusters would be much harder. You'd have to deal with the original timeline that goes The Real Ghostbusters (including all pre-IDW tie-in media) then Extreme Ghostbusters (with IDW tie-in media), as well as the alternate version that doesn't lead to Extreme Ghostbusters, which is The Real Ghostbusters including both pre-IDW and IDW comics.
That's because IDW placed them in separate realities while acknowledging that The Real Ghostbusters is still technically the past of Extreme Ghostbusters. It's possible the Mars Attacks crossover occurs in both realities I suppose, though I could be wrong.