If you ask me, what action should I take at that moment? I will definitely choose to decide depending on my situation. Fighting against corruption in a corrupt country is really not an easy task. But in reality, it might be a good step for you to form an organization to fight against corruption, with which you can fight against the corruptors for a while and get some media attention. When you fight against corruption and get some media attention, you might be a little safer and your family will also get protection from the country.
I can't say what the situation is like in your country. But I will definitely try to fight against corruption by using some money from the side of corruption, out of morality, and I think it will be legal for me to use that money. Sometimes, corruption has to be made a weapon and fight against corruption. In essence, your friend can gain the ability to fight against corruption with the money of corruption, where there will be little risk to him and his family.
You are fighting a corrupt system with corrupt law enforcement agencies and compromised court. The police is controlled by corrupt politicians and the court give favorable judgement to the highest bidder. The press lack freedom and most journalist are intimidated a s others are sent to prison for saying the truth.
The only way to fight the system is to leave the country with your family and expose the corrupt system from the country your moved to. Most truthful journalist on my country have left the country so that they can be free from intimidation. Or you decide to sacrifice your life and be willing to accept any consequence..