Family Issues Support Group
Family issues is a huge range that go from minor conflict to major misbehaviour and even abuse on the part of individual members of the family occur. Whether you feel you are in a dysfunctional family or you're dealing with a very specific issue, this is the place to talk about it and find others who might be going through the same thing.
You mention having younger sisters. They would be school age, so go to their school counselors or administrators. They are required by law to intervene and find help.
Please reach out for help. The internet cannot give you the kind of help that you need. You need flesh and blood people who can help you work out these problems.
As to my sisters, we are living in a very poor state. Such help was never a privilege for us. As far as I know we can handle it, just not when he is around. It's really hard.
Who cares about a scandal? It'll be HIS reputation that's shot, NOT yours. He's probably banking on this, so it'll really shock him when you say, "I don't care WHO finds out!"
Get some documentation of it and go to the authorities.
And please don't feel guilty. You're not a bad person. You just want some peace, and his death would be one way for that to happen.
I was there, once, too.
Also you aren't a bad person for wishing your dad were dead. You have your reasons and he is not a good person.