Q: How to install multiple versions of Delphi on the same machine?
The same installation of WPTools can be used by the different Delphi installations. Please just make sure the search path lists the correct sub directory.
When you switch to another Delphi version than the one you used before, you will likely have to use "Build All" on your project.
If you use a different project files for each Delphi version you can use an output directory to create object files individually for each version.