Creating Revit families from imported CAD geometry from other CAD systems (e.g. DWG files, for example) has many limitations, two of which you have discovered.
RFA files created by importing CAD also tend to be quite large, and can't be parametric (require many RFA files to handle different sizes where 1 parametric one with different types in it can do the job). I believe they can also slow the project's performance down significantly as well.
Generally speaking, Revit families should always be created by drawing them natively in Revit, from scratch. That would definitely solve the issues you've discovered as well.
So the answer to your question is: What you want to do cannot be done in family files whose geometry is imported CAD from other systems.
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