I have a G7 Panasonic. That records 1080p 50f.
I have a G85 Panasonic That records at 1080 60f.
I have Go Pro 9/10 which is... well a go pro.
I have gone back to 1080p on my cameras because of colour richness and also focus.
However I want to be able to use G85 at 60f and G7 at 50f ... to create the video.
Surely if I mix the frame rates - and drop those into a FCP timeline my voice in the audio will differ between the cameras. Is the only option to try and shoot with only one camera.. and then use that frame rate for the edit?
The audio won't be a problem but the video may well be.
I know for a fact the GoPro can do 50fps and 60fps no probs, and the other two should do as well. If they're anything like Sony prosumer cameras, the Pannys might be changeable somewhere else in the menus. Look for something that says something like "PAL/NTSC" or "Region," although I fear that these may have been removed on some North American models.
If not, I would strongly recommend deciding on the frame rate of your timeline (60 FPS in North America/Japan or 50 fps in almost everywhere else) and re-encoding to ProRes the offending footage (all the footage even better) using Compressor or (my fave) Shutter Encoder before you start editing.
In my experience if you are forced to mix frame rates you are unlikely so see issues on shots with little movement so I'd opt for the frame rate of the camera seeing most action for your project. Failing that I'd expect 60 fps to reduce better to 50 than the other way around.