@sjsm,
Ask your sisters to call CPS. Most courts will allow a 16 year old decide who to live with, providing they can provide suitable support. Is there an adult at school who can assist, guidance counselor, trusted teacher?
I don't think your idiot stepfather can actually drop you off at juvenile, what will he tell the authorities, "I don't like him to be in the car?", however, I would not pin all my hopes on everyone recognizing this man to be such a control freak. See if your siblings can do some research on your behalf. Since you father died before you turned 18, you are entitled to social security benefits. This money can only legally be used by you. Your stepfather may be intercepting the checks and using them for his personal benefit. Your siblings should look into this for you.
The reason I'm suggesting your siblings do these things on your behalf is to prevent you from any negative fallout from your stepdad or mother. I don't know why they insist you stay with them, but I am deeply suspicious. It is vital that you proceed carefully and with a plan. You may even need a lawyer who can make sure your rights and well being are properly protected.
Please proceed carefully, you are absolutely entitled to a better life, try not to give in to despair (I know it won't be easy) but you are not property, you are a minor but no one should have to deal with the mental and verbal abuse. Another thing to remember, your stepfather has no standing to make decisions for you. Unfortunately your mother seems under his control and I doubt she will be of any help and will defer to his opinion.
Make sure your computer doesn't reveal anything that would anger the stepfather, be careful, please.