Hello! Welcome officially to the forums!
One mistake I made with my Mother, was that in my eagerness and hope that she'd see things as I did - was to overload her with all different facts, my mother isn't an active Witness, but she is a born-in and has been for 40+ years. While I still pray & have hope that she will come to see the truth about things in time, I'll admit I made a big mistake doing what I did. Don't overload them with facts all at once!
Honestly you could approach this in a few different ways, a single topic to kind of break the ice, depending on what you think matters the most to THEM
- The Child Abuse/Sexual Assault
-The discrepancy of 607 BCE - 1914
-The false end time predictions
-Discrepancies within what the Watchtower teaches vs the Scriptures (two big ones for me was the context of the "light getting brighter" & the partakers of the Passover)
You know your parents the best. Any of these could really create a lightbulb effect and get them to either question and examine the scriptures, or if its more about the scandals, look up news articles.
We all have different things that "woke us up" so to speak. Mine was more of an emotional "no loving God could destroy 99.9% of earth due to a technicality of not being part of a man made org."
Find theirs and try to gently slide it into a conversation, you really don't want to make it seem like you are attacking their beliefs, because that will only cause them to close up.