To answer this type of question, you have to consider the way that the author has written the characters. Do you believe that these characters have hopes for families in their future? To ask if they will get married and have children suggests a hope for a more fulfilling adulthood. The childhood experience for all of them has been dysfunctional. The Curtis brothers lost their parents; Two-Bit is from a single parent family; Johnny's parents were abusive. To get married and have children will to be creating their own complete family unit. Does Hinton suggest at the end of the book that there is hope for such a happy future?
I would argue that there is. In the end, Ponyboy is acting out and there is still tension and fighting in the Curtis household, just as there was at the beginning. But then, Sodapop breaks down, and the brothers have an epiphany. Just like in the beginning, one brother runs out of the house - however, this time, the others follow and catch up. That is more hopeful than earlier in the story. In addition, Ponyboy actually tells us that he understands now - understands what has happened, understands that things can still be ok now. Then, he and Darry promise Soda to try to do better, understand each other more. That is pretty hopeful. And the fact that Ponyboy goes home to write something that could be helpful to others also suggests that he is ready to find happiness, to be a leader.. and maybe someday a father:
"I could picture hundreds and hundreds of boys living on the wrong sides of cities ... There should be some help, someone should tell them before it was too late."
On a more literal note, just the character of Sodapop suggests that the boys will marry and/or have kids one day. He is ready - even eager - to marry Sandy when she says she is pregnant with his baby. He is all set to step into that role, and is very upset when it is taken away from him by her confession. Readers can assume he'll find another girl to love and to give him this chance at some point.