I will tell you what you should do:
If your dad is beating you...call child services. They will help you out. No kid should ever be beaten. EVER. A threat is almost just as bad as doing it. It makes you live in fear when he should be the one that is supposed to be providing a safe and comfortable shelter for you.
If he wants to put you in a situation where you are coming to physical harm: call child services. Bringing someone into the house that makes advances on you, gets drunk with her friends/ your father....is not a healthy environment for a child/teen.
It seems like you've tried to talk to your dad about this unhealthy relationship with this woman, so maybe reasoning with him is not the answer. You can tell him one more time that if anything else goes wrong, you will make the call on him.
Or, you can just safely call child services and tell nothing about it to him, and explain the situation to them. I don't think that's out of order.