Why was the extended family important in slave life?

Family life was important to slaves because it was just about the only thing not regulated (at least not entirely) by their masters. By creating extended families among themselves, they kept their spirits up and felt like human beings, not like property. They constructed these extended families also because their masters did control them to some extent, in that they could be sold off and separated from their real families, so the other slaves became their surrogate families.