Not sure about questions to ask but I would want to hear from the doctors whether:
a) adding another kind of hormone (casodex) to the existing one might slow the progression down a bit
b) whether the liver spread means that alternatives such as enzalutimide, abiraterone or radium 223 are now not possible
c) whether chemotherapy is a possibility
I would also want to ask whether the situation is now serious enough for dad to be considered more advanced than 'incurable' - if so, he might want to consider applying for some disability benefits from the Government. Also, if not already done then you could ask about a referral to Macmillan or a nearby hospice; they can help with things like practical arrangements, massage, aromatherapy, counselling for family members and pain relief (if there is a lot of pain and it is proving hard to control). Hospices should not be a frightening word - they can do lots to support people dealing with cancer and are not just for the end of someone's life.