First if all you should have concrete evidence against that person before accusing him of doing black magic, then another concrete evidence that he is doing it against your father. Before have such concrete evidence against that person, you might fall in a major sin of putting allegation on that person.
You have no right to tell any one about what you think about that person before having the concrete evidence against him.
As far as the black magic which you think is done against your father and his family, the remedy is the same whether it was really done by any one or not. Even if it was not done, it is useful to protect your family by the same recitations which are: Sura Al-Falaq and Sura A-Naas to be recited after every prayer and before going to bed three times, as well as Ayatul Kursi. Sadaqa is also very useful in protection from evil.
We must refrain from any sinful act even if family and friends insist in it. You must refuse any sinful act. No one is more important to obey more than Allah (SWT). We disobey every one but never disobey Allah (SWT).
Different people look at a thing and take different lessons from it.
However, one could glean from their marriage that when two people are sincere, mutually self-sacrificing, pool their wealth and talents, and committed to each other and a higher cause, they can accomplish anything!
I am sure there will be some other insights as well.
Read what the Prophet (SAWA) and his Progeny (AS) said about treating your family (Best of you are those who are the best in treating their families).
You need also to read about the bad results of being toxic to your family e.g. miserable situation in the grave, etc.
'We need to be humble inside our hearts and believe that our family members are humans like us and part of us. We deal Wi them as we want them to deal with us. We will enjoy life here and hereafter if we treat others nicely especially our family.
Try to look at the mirror if you become angry, you should calm down because you will see how ugly to be angry.
Keep on seeking forgiveness for the past and seeking help of Allah to make you a nice person with your family.
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