If all you want is 12 separate processes each running file2.pl then you don't need threads in file1.pl.

I find that simple solutions are easier to write and maintain than more complex solutions. Therefore, I would not use threads in file1.pl unless there was a compelling reason for them. I suggest you think carefully about why you want to use threads. Maybe it's not necessary.

If you explain why system and fork are inadequate for your needs, it will be easier to provide helpful suggestions.