I have led a women's group for 5 or so years, and last year two Catholics began to attend. I never debated anything with them. But in teaching the message of grace, one of them totally got it, and it changed her life. She even went to her mother with the scriptures concerning grace, and her mother was overwhelmed with this knowledge.
The truth has its own power when presented with love. We don't have to argue on points where we might differ.