There is information missing. It might be that the cancer has spread further than dad told you, or he has agreed with the onco that he doesn’t want any other treatments? With his consent, the onco might agree to speak to you. Has he been referred to a hospice or palliative care team? If so, you might be able to get more information from them. Could dad have misunderstood?
If he only has a few months to live, he is entitled to payments from the government. The hospice or a Macmillan nurse can help him fill in the application forms - the money can be used to buy equipment he might need or to pay for night sitters if he chooses to stay at home at the end. Macmillan or the hospice staff will also help you as a family talk about any arrangements like how your dad would like the end to be.