Do you want this guy back in your life or not?
If you do, set firm conditions, send them then do not respond untill they are met.
One firm conditions would be to not harass 3rd parties by him or agents of him.
Personally, I'd set a firm condition to never text you. It's a form of 'immediate' harassment.
Instead, I'd set an email address for him, that you check at your own discretion. Every three months at most. Even better. Set up a private subreddit. Let him post, and when he's being an ass, downvote him.
Personally, I'd just cut him out forever.
People like your dad always seem to think that they are better than everyone and at worst, equal to everyone else.
He thinks you're on level ground which he is not. He's got to come up to your level.
Instead he thinks that he can approach you without 'rising up' or changing.
I hate people like this.
They think that 'wanting' to repair a relationship somehow makes them worthy enough to be a person worth repairing a relationship for and rights all the wrongs.
A proper reconcilliation doesn't start with "I would like to resolve the issues we have if you are willing to resolve them."
I'm going to be a bit heated when I say "Fuck you. 'we' don't have issues. I didn't do anything to contribute to the 'we' issue, therefore there is no 'we' issue. Do not make me responsible for what are clearly 'your' issues. Take responsibility for the 'your' issues, and don't you dare make me do any of your work.
A proper reconcilliations start with "You are angry because of what I have done. What I have done is "x" and as such, have done 'y' to resolve them. I would like to tell you what 'x' has done to damage our relationship and to explain how it has been very harmful to you and to apologize for such actions. If you do not wish to meet, I understand, and in the absence of, I will continue to work on 'y', not to gain favour from you, but because it shows me the error of my ways and teaches me to not be the asshole I was and still am to a certain extent. If I come to a better understanding, and have incorporated it as a better way to be, I would like to contact you again. I wish to make you feel not harassed, and will keep a very low contact. In the absence of me contacting you, I will have a twitter feed/subreddit of my therapy. It will document my mistakes and restitution. In your absence, I hope it will be a document that best will show that I am changing for the better, and at worst haven't changed at all. It will be the record I need to show me the progress I have or have not made. You are welcome to read it or not. Thank you for your consideration."
See, an apology like that doesn't make the OP responsible for anything.
Although that will probably never happen.
Dad needs to start working on himself and leave OP alone untill Dad self improves.