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If possible never let them sit too close to each other.
All kids who live in the same house should have restraining orders. Look at the definition I googled:

"What is a restraining order?
A restraining order is an order made by a court to protect a person from physical pain or injury or the threat of pain or injury. It can generally be issued against a family member (for example, husband, ex-husband, father of your child) or a household member (anyone with whom you live or used to live) or against someone you have recently dated. You do not have to be married to the person to get a restraining order. However, you must know where the person lives or works. A list of the people against whom restraining orders can be issued is on the restraining order form."

Don't brothers and sisters, when they are children, hurt and bother each other? So, a restraining order would be perfect.