Delaware rental rules? what can be done with celling collapsing, flooding and mold?

I have a friend in Delaware who lives with his elderly grandmother. They rent a house. The mother is distant and is in charge of the paperwork, power of attorney, etc. The roof is currently collapsing and there is flooding in the basement with mold. I don't know the entire situation, but apparently, the Landlord isn't doing anything.

What else can they do?