Asking about Parent-Child relationship karma. Is it bad if I don't wanna go visit my dad?
Your question is very important, but difficult to answer, since within Buddhism answers are not always what we want to hear.
Your father and his family members are experiencing there own karma, which in this case is not good for them or pleasant for others.
Within yourself you should try to find loving-kindness for their suffering. You can accomplish this by realizing that the bad manner that they use with you is a lesson in how not to behave. Try to find compassion. This will help your mind to accept, and realize that your visit with them is temporary...when it is over do not dwell on it.
In Tibetan buddhism all sentient beings were once our kind and loving mothers. We try to remember that in our dealings with others. It is not always easy, but you will be a better person if you have compassion for all others.