You have to pick these options from my experience
You must be a helot
Choose to listen twice, when eavesdropping
feel exhilirated and listen intently to the story
Then make sure you continue singing loudly
He should escape whilst guard focuses on you.
I dont think it matters what you say to your Dad, I usually grunt noncomitally but I dont think it effects it.
He also will join you later in the story, but from my experience once again, you must have low anarchy and be popular with the yeomanry. I think it also helps to be Shayard loving, but overall, I’m not sure the exact triggers. I just know he joined me in my pacifist run, and he does help.