How do I deal with my father who is immoral and outside the bounds of Allah’s law, while I fear for myself because of him?

The transgression of parents does not absolve children from being dutiful to them. It is therefore obligatory to treat the parent with kindness and respect, while also being obligated to advise them with a good and appropriate approach. If you fear for yourself from merely denouncing their act, then it suffices for you to denounce it in your heart, while not partaking in their transgression. If you treat your father with kindness and denounce his act to the best of your ability, then there is nothing held against you thereafter.