Do you know where it has spread to Katie? If it is advanced and he has been told it is terminal but his bone scan was clear then they must have found spread in his liver, lungs or somewhere like that? As harsh as it seems, if he has indeed been told he is terminally ill then his care will not be led by an oncologist ... they usually get involved with cancer patients for whom there are still treatment options. 'Terminal' is usually used to refer to men who have such serious spread that they have no treatment options and will only be offered pain relief, and this is usually led by the local hospice team or Macmillan nurses.
So as horrible as this is for you and for dad, the referral to Macmillan (which it seems has already been done) is the most important thing and they are usually very good at getting the pain relief sorted out. It is very hard to get a balance between being in pain and being so drugged up that dad just sleeps all the time - the nurses should lead on this with dad's GP, not the hospital so I don't think a complaint to PALS would really help.
Macmillan will also be able to advise on how dad should go about claiming benefits. This money, available for people who are terminally ill, can be used to buy equipment that will make his life easier, or helps cover the cost of family members being off work to help care for him, or to pay for professional care / help in the house if and when he needs it.