If I deal with usurious banks and withdraw money without knowing the exact amount of interest, and my family deposits money in the bank periodically against my will, how do I get rid of this interest?

All praise is due to Allah, and may peace and blessings be upon the Messenger of Allah. If a person has unlawful wealth and is ignorant of its amount, they must strive diligently, exercise caution, and spend what they believe will clear their conscience. If the wealth is from usury, they should return it to its owner; if they cannot find the owner, they should give it away as charity on their behalf. If the wealth was taken through injustice, they should return it to its rightful owner. If they do not know the amount of unlawful wealth from the lawful, they should investigate and spend what they believe will suffice until they are certain that what remains is lawful for them.