There's only one Ghostbusters movie being made
The initial rumours started a few years back when the second sequel to the original movie was touted then slowly morphed into more of a reboot. Recently, writer Drew Pearce has reignited these rumours by talking about how he has been creating a 'bible' for a second Ghostbusters flick. This would be a piece of research which would come before a script, making sure that the details of a universe are consistent across multiple movies.
But it seems there's no second movie on the way, at least according to someone who should know. Original Ghostbusters director Ivan Reitman is a producer on the Paul Feig film and he's released a statement about the news: