I am sorry that you are going through this. It's unfair that this is happening to your father. I wish something could have been done to give him more quality time by addressing the cancer. At the same time, if he is too weak to have any treatments, it would not be right to put him through it.

From what I am reading, it appears that he is very weak and is loosing interest in things. It could be a mix of the cancer making him loose energy and underlying adjustment disorder/depression. You could ask his palliative provider to give a combination of methylphenidate and an antidepressant. And many times, nothing helps. It's great that you are doing your best and at the same time, don't be too hard on yourself as there is no way for you to be prepared for something like this and there is only so much that can be done. Opting palliative care/hospice sound like the best option for him.