Refer to question that led me to ask this question How to call out narcissistic father on emotionally blackmailing my sister
I am considering calling the police station to explain my situation and asking for advice, but I want to have a planned explanation why they should take me seriously. I have reason to doubt that police officers in general do not get involved with personal disputes with family members unless they are threatening bodily harm.
Because of this, I need a bit more preparation and consideration before I do this.
TL;DR: My sister has her things at my dad's house, my dad won't give her things back until she gives in and lets him see her in person.
What points do I need to consider for speaking with a person of authority about an emotional issue between my dad and my sister, and asking for their intervention?
If anyone has a frame challenge ("this is not a good idea") please explain your thoughts fully instead of "don't do this!" as an answer.