Chicory, I can feel your pain and I'm so sorry. I know how maddening it is when someone you love and cares for just throws all that love back in your face with disrespect, derision, and just selfish, irrational thinking (believe it or not, I'm not thinking of my AH, I'm thinking specifically of my younger brother who sounds a LOT like your son). But for the most part, that's the disease!
I don't know what to tell you about October 1. Step 1, as you said, is just getting him out the door, which I realize will be painfully difficult for you if he does not go willingly. Do you have any support there who could be there to reinforce your resolve? How about having someone you love and trust stay with you for a day, tell him on September 30 that you expect him to be out, and then if he defies that, just wait until he leaves the house and then change the locks and put his stuff out on the lawn? I know that sounds really harsh, but he's had plenty of time to get the message. My MIL did that with her brother, and he wound up fine. He got himself an apartment and eventually moved to Florida to be with his kids.
Your son has his own HP. Trust that.
Once he's gone, it will be SO much easier for you to put this all behind you and lead your own life.