How can one treat an oppressive father for whom there is no love or affection in the heart, without falling into the sin of undutifulness to parents?

If a father slanders chaste women, curses unjustly, and falls short in spending, then he is an oppressor and commits major sins. Despite this, his right to dutifulness and maintaining ties remains, and he must be accompanied with kindness. Part of being dutiful to him is advising him and warning him about these major sins with politeness and gentleness. Disliking the father because of his abominable actions does not cause harm, as long as the children uphold their dutifulness towards him.