I don’t know about event only recordings, but with continuous recordings, you very much can see footage from a different camera if you move the uSD card from one camera to another.
And yes, the camera will delete the oldest recordings when it runs out of space.
I have never tested to see if it only overwrites the footage from the new cam only. Let us know what you find out when it starts to overwrite.
I would suspect it is going to overwrite the files from the older cam first. This is because the cams don’t save the MP4 files to different folders or segregate them by cam type or MAC. They all use the same file path: Root \ record \ {year YYYYMMDD} \ {hour#} \ {minute#}.MP4 to save the SD video footage.