So sorry to read this its so hard hearing this news but my personal advice is to cherish every moment take photos, videos as much as you can and if there is no hope then to be happy ypu have had your dad around for so long i no its still *** but it helped me thinking like that a little anyways.

My Dad suffered for 2 years he had Chemo, immunotherophy and then Radio which i think finally killed him off he was 52 and he lost his speech due to Radio but everyone is different and if it had helped then id have been happy but he deteriated only advice i can ever give is honestly ask the questions you want to ask now and note them and ask about funeral plans as my Dad made plans but we were confussed as to why he changed his mind last minute to cremation i was always under the impresstion he wanted a buriel and this dissapointed me as i feel i have no where to go to grieve.

Be strong and ask every awkward question you want to i feel comfort from videos and photos.