I was actually curious to see what this looked like, so I did one!
So not much overlap for this one. AP/FF have overlap around Werribee, but FF and GW have a decent amount in the inner -mid south eastern suburbs.
I also did a 90 minute one, which I think is the maximum most people would be willing to drive to go to one of these parks:
So Funfields and Gumbuya end up being within reach of virtually all of metro Melbourne, but Adventure Park only reaches to the inner eastern suburbs and some of the Mornington Peninsula (the map even takes the ferry trip into account!). It's also almost reaches Ballarat. Also interesting is that Funfields almost reaches Shepparton in 90mins while actually reaching the Geelong CBD also. Gumbuya almost reaches Sale (and covers most of SE Gippsland and the Latrobe Valley).