My family member is working in my buisness. How do I ask for rent that I need?

I've been in this buisness for a long time. I need to make it clear that I need rent from this realitive for the space that is used, it's buisness. I know they are having finacial difficulties but if this continues I will be in the same boat. I could rent this space to someone who is serious about making money. Help!