Let me see if I understand this:

1. You have an application that isn't Perl.
2. You run from this application some Perl script.
3. From the Perl script, you launch another Perl script.
4. The parent and child scripts talk to one another.
5. At some point, you wish to be able to launch a grandchild script.
6. This grandchild script may or may not need to be able to talk to the child script.

*blinks* I'm going to say right now that this is starting to sound like a poorly-designed application. Without seeing your code, I'm going to bet that you are calling the grandchild script when you probably should have it as a module that you use in the child script. I'm guessing that you have these grandchildren scripts to add functionality, depending on a series of possible outcomes.

It sounds like you may need to explore modules and redesign the way you're doing things.

(Please note that you have given very little information about what you're doing and how it's implemented. If you know about modules and are using them, then I apologize for any insult you may feel I have given you.)