How to Join / Trim the Haunchs and Rigid frame column ?

I guess you want to extend the column to the beam, correct?

Try to use the Modify tool 'Extend/Trim to Object'. Screenshot below:

Where you want to add stiffener plate (at top beam, collumn)? or make connection beam/collumn with plates? Check the 'ConnectionCenter' for existing connections (menu ProStructures->Steel Connections->Miscellaneous->Stiffeners).

Hope this helps.

Regards,
Darius