How is the theme the importance of family shown at the point when Ponyboy and Sodapop might get put in an orphanage in The Outsiders?

Ponyboy is worried about losing his family because his brothers are all he has.

Ponyboy’s parents died in a car accident, leaving his older brother Darry guardian of Soda and Ponyboy.  Darry is only twenty, and not much older than his brothers.  Pony and Darry are constantly arguing, but the most important thing for the Curtis family is to stay together.

When Pony and Johnny are attacked by a group of Socs in the park, Johnny kills one that is drowning Pony.  The two boys go on the run, and end up in an abandoned church.  The church catches fire and they get hurt trying to rescue a group of children who get caught in it.

The incident puts an end to their running.  Johnny is badly injured, so he is never charged.  Pony, Johnny, and Dally get a lot of publicity.  Pony worries about what the close scrutiny could do to their family.

If the judge decides Darry isn't a good guardian or something, I'm liable to get stuck in a home somewhere. That's the rotten part of this deal. Darry is a good guardian; he makes me study and knows where I am and who I'm with all the time. (Ch. 11)

Darry certainly grew up fast.  He got a job and took care of his brothers.  Soda dropped out of high school, but Soda was never much of a scholar.  Pony, the youngest, got A’s in school and was in honors classes.  As far as he was concerned, the three of them were doing just fine.

Darry and Pony often argued.  In fact, it was a fight where Darry hit Pony that led him to that park in the middle of the night in the first place.  After all that happened, Pony wants to avoid fighting so much since they are back together.

We couldn't do anything to hurt Soda. Sodapop would always be the middleman, but that didn't mean he had to keep getting pulled apart. Instead of Darry and me pulling me apart, he'd be pulling us together. (Ch. 12)

Family is very important to Pony and to his brothers.  They are a family, even though there are no parents.  The loyalty the greasers have for each other is also a type of family.  They have to stick up for each other, because no one else will.