I start enzo in two weeks and I have been told we would know within four weeks if it is likely to have an impact, as the entries above suggest. It looks like your Dad has a very agreesive cancer as the main treatments have had little impact. Have they talked about radium 223 which I understand, though I am no medic, works best when the cancer is active. Might be worth an ask.
If he is reaching end of life stage as the onco is suggesting, you will need to ensure he gets all the care he needs to help you and your family care for him. So think about Macmillan nurses or equivalent and hospice care. It is important to be prepared. Keep in touch with us on here many have been through this difficult time and are very supportive.
Fingers crossed for enzo.