Use a different PGraphics for each player.

But so do I have to store all the other stuff as bullets or map in both of the PGraphics ?

No. Most of the things you have (all the game relevant objects) can be stored once. The only thing is that instead of drawing to the main PGraphics in the draw() loop, you draw to a player's PGraphics with the input parameter for the individual camera() settings. The per-player draw() can be identical, except that it has parameters for the camera view and it operates on a PGraphics instead of the main PGraphics.

As an alternative you can use direct opengl calls (but that usually leads to more problems down the road).

Check out this thread:
https://forum.processing.org/topic/set-3-viewports-from-3-camera-s-pointing-the-same-object

Sorry but when I set camera() for the first player PGraphics, it sets the same one for the second.

Seems you are connecting them by reference through test. Really make them two seperate PGraphics .See the example on the page I linked to earlier.

Sorry again, but in your example, you write several time the same object so it means that I have to write everything twice ?

No, what you need is a single drawEverything(playerPGraphics, inputPlayerCameraSettings) method, that you only write once. Then it can be used multiple times, as shown in my example. You will notice that it has 4 screens, but only 1 drawCube() method. Each individual PGraphics makes use of the same drawCube() method, but with different input parameters (the PGraphics being one of the input parameters).

What you are trying to do is draw everything and then set different cameras in different PGraphics. This is NOT possible. You can't change the camera after you've drawn the scene, because the camera determines HOW the scene is drawn. This means you will need to completely redraw the scene for each individual camera. That's the bad news. The good news however, is that you can do this with relatively short code, namely as described above.

I finally managed to do it, thank you so much !