Family is represented by the closeness of Kino to his wife and baby, and his desire to help Coyotito.
The first demonstration of family is in the first sentence, which focuses not just on Kino, but on his family.
"In the town they tell the story of the great pearl - how it was found and how it was lost again. They tell of Kino, the fisherman, and of his wife, Juana, and of the baby, Coyotito. (ch 1)
The opening scenes of the book are resplendent with simple domestic tranquility that shows that Juana loves Kino and he loves her, and they both love Coyotito. Kino describes it as the family song.
And this was part of the family song too. It was all part. Sometimes it rose to an aching chord that caught the throat, saying this is safety, this is warmth, this is the Whole. (ch 1)
Unfortunately, little Coyotito gets stung by a scorpion. Juana acts quickly, sucking the poison out, while Kino helplessly crushes the offending insect to bits. Their perfect life is no more, as everything they do is focused on Coyotito. This is part of being a family too. Family is enjoying the ones you love, and doing anything to protect them.