Modern phone cameras are 99% software at this point. If you took one phones camera and put it onto another phone without adapting the software then the photos will look like ass.

You can’t just unplug something from device X and connect it to device Y. The connectors aren’t standardized. And even if they were they wouldn’t fit because the placement is different. In theory you could take the CPU off of one device and plant it onto another. But have fun with that BGA micro soldering. Plus the connections will be different unless you picked a phone with the exact same CPU. Ram is the only thing you could potentially upgrade. But like good luck.

You’d legitimately have an easier time making a new phone from scratch than trying to piece together 3 different phones.