How to use units in delphi project group

I have a group of projects with 3 projects (standAlone, ISAPI, module for apache), until now they all have the same file.pas and when modifying code and compiling the .exe, the .dll and .so are updated.

I want to add another unit (.pas file) to better organize classes and make it easier to navigate through the project code.

My question is, should I add the new file.pas to the three projects or only to the standAlone? (use RAD Studio 10.2)