so take a look at THIS LINK
pay particular attention to the paragraph that starts..... "Usual Generic Dose for Pain..."
you will see a sentence that says that for the immediate release form, which it sounds like your dad is on, 'doses of greater than 30mg are rarely needed and should be used with great caution....'' in short, there is no good evidence that doses over 30mg at a time are any more pain relieving than 30mg alone. the fact that your dad seems ONLY to be on opiates for pain is another red flag. this treatment may be malpractice, but it is not 'illegal' in the criminal sense.
if you wish to pursue legal action then you might have a case and getting a pain specialist involved would both help your dad and give you an idea if legal action were likely to succeed.
from what you have told me your dad has been mismanaged. having been in the doctor side of the equation you do not have nearly enough information to go to court and, if you did, you might very well find that your dad would testify on his doctor's behalf if you could somehow sue him for malpractice.
i am sorry, this is terrible.
let me know if you have further questions. 'excellent' feedback is always appreciated.