Susanna,
Not to discourage you, but I just lost my husband on the 7th of December. But as to your question about how much, oh my gosh, my husband the last week was on 300mg of fentanyl and up to 40 liquid morphine, every hour as needed. Granted my husband started out as 300lb @ 6'4", sadly he lost over 100 lb in 6 short weeks. My point being, do let him suffer, at first my husband would tough it out, but I could always tell when he was in pain. Although he would not accept it from me, whereas, my brother in law, who filled in for me, would push the meds on him and my husband would take it. In my husband's final night, he was on a pump of morphine, every hour, accepting manually pushes every 15 minutes, he was in a great amount of pain, almost in a half sedated, unconscious state, he would groan in pain, even then. This disease is horrible, do not let your dad suffer in pain.
Wisdom to you.