Dad mentally, verbally, and sometimes physically abuses my family.

My dad is awful behind closed doors. He's a cop (not working as one right now but still certified), he's a Paramedic, and a firefighter. Everyone thinks he is the most amazing thing to walk the earth, as he portrays himself that way. But when he's home, its a whole different story. My siblings have been called every name in the whole book. He calls my little sister a waste of life, a bitch, psychotic. I have him on video screaming at my mom calling all of us pieces of shit and everything else you can think of. He's held my mom down before screaming at her and pushed her and fought with her in our front yard. But, we're not allowed to tell. My mom says we're not allowed to tell my grandparents or anyone else. My dad threatens us and tells us what he'd do to us if we told. My question is... Does anyone have any police officer parents, friends, or you are one that could say if something might actually happen if I did tell. We live in a small town and I'm friends with the chief of police (so is he) and he's only one call away. Should I make it?