For 8 cameras ? Forget it.
If you want more or less reliable detection from cameras, then you need to use machine learning. There’s just no way around this. That means using something like Deepstack, Frigate, DOODS, etc. Under the hood they’re all pretty much the same and use a pretrained neural net for person detection. And that is a very performance heavy operation. Using a Pi to do that for a single camera (and without an additional tensor processing unit like the Coral) is bad enough. Doing it for 8 is impossible.
So either switch to more powerful hardware or rely on a different motion detection technology (PIRs, radar, lidar, etc).