do you think $15,000 then yearly payments of maybe $3,000 is fair? Do I need an attorney to make the offer?

Let me work backwards in answering your question.
You don't need an attorney to make an offer - you can contact your father, or his attorney (if he is being represented, contact his attorney) and make a settlement offer. However, it will probably seem more professional (and seem like you are more serious) if you have an attorney do this for you.
In terms of what is "fair": to be honest with you, it doesn't matter what I think is fair. All that matters is what your father would be willing to accept. Think about getting into his head and making him an offer that you think he would be willing to accept. Good luck.

Thank you so much for answering. I do believe my father wants the full amount. Is it acceptable to offer payments. There is no way I can come up with that much money. What would happen if he would refuse the offer? This is a horrible situation for me;thank you for being helpful.

I'm happy to help. I think it is a great idea to offer payments. If he doesn't accept, I assume he will continue to pursue litigation.