I'm sorry you're going through this. It's clear that your father is terminal. You and the rest of your family, including your father, have to come to terms with this. This is coming. Denying it won't put it off.
The most important thing to address is what your father wants in his last days. What does he want to do or see? Are there places he would like to go while he still can? You and your family have a responsibility to make these things happen for him, at least as much as you can.
Has your father made his last will and testament? Even if you don't get a lawyer involved, you need to make sure his final wishes for the distribution of his estate, even if his estate is only, like my mom's, a couple of cabinets and a pile of old quilts.
Has your father made arrangements for a funeral or memorial service? What does he want to happen to his remains? Make sure this is done so you don't have to worry about it in the aftermath of his death.
Most importantly, spend time with him. Even if your own feelings are complex, make sure that he knows that you love him, that you value him and that you aren't going to forget him. Do what you can to help him feel happy and at peace with himself. This is not the time to be selfish or to vent old frustrations. This time is all about him and what he needs.
And also make sure, on your own time, to take care of yourself and your loved ones. Grieve. Find the path to acceptance. Your father is going to die. Accept that, find your peace with it and move on.
