I have a cousin who has a money problem with somebody and may be the police will take him to the prison. I haven't money to help him, but I can borrow from a bank to help him. This loan will be with interest. Does Islam allow me to borrow from the bank with interest to help him in this case?

Praise be to Allah, the Lord of the World; and blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
You are not permitted to borrow money with interest. Dealing with interests is a great sin and it does not solve the problems rather makes the problems worse, more complicated and more dangerous.
Moreover, any money, which mixes with interests, will be destroyed.
Therefore, the Muslim is obliged to avoid interest completely.
Allah knows best.