Maybe you will require two Faraday cages, one for WiFi and the other for GPS.

You might want to see of there is an advantage of having two separate circuit boards, one for each module. If that turned out to give benefit you can make the equivalent of two circuit boards on one PCB by splitting the GND/PWR planes between the two functions and not allow any signals on other traces to snake through these regions. Have the power and signals feed into the two modules from a common part of the board where you also place the filtering networks for going into and out of each module.

If these modules are purchased assemblies it should be easy to try them out as independent assemblies......although you have probably already spent hours doing this already.

Michael Karas