The family is the most important social unit. In my experience, Family are the folks I turn to when I'm in the most need.
The ultimate goal of any society is to reach the status of one big family, but Society and Family are two different social units (thus is why Strengthening Society is its own value). In a basic sense: Society is a greater unit than one you can unconditionally care for. Family requires unconditional caring. It's impossible to care for everyone in my society as much as I care for my grandma or brother, for instance. For that reason, I might as well add another value Strengthening Friendships).
I should also note that the role of a husband or father is part of family, but a bit different. For that I have created Strengthening My Love Partnership and Being the Best Dad.