Hi Barry, Greetings from Australia

If you run the same program on all four pics the result will be the same.
There is no math formula to produce a random number
PicBasic will cycle through a finite set of numbers.

If you can choose a seed, you could load each pic with a different seed.

If any action depends on a user pressing a button you can time the button
push, or count contact bounce, and add that result to a seed for a different seed each launch.

Without any external input, I think you'd be needing to at least write
something different to each on-board EEPROM,
unless you can do something really tricky to detect noise in a power supply or some such thing.
Cheers, Art.