Here is how things would be if you were his younger and older sister. 

Dallas

Older: Nagging at him not to get into fights and think about his future more. He's grumble and mutter whenever you'd go near him because you complain a bunch about what he is doing. You remind him of your mother before she died. 

Younger: You'd want to follow him around all the time. When you would get into trouble from taking after him, he'd get you out of it but then tell you to beat it. He would see you as an annoyance. 

***

Ponyboy

Older: Be overprotective of him whenever he'd get a scratch or bruise. You'd stick up for him whenever a soc or Steve would fight with him. Ponyboy would get so embarrassed at it, because he thinks he doesn't need a girl to stick up for him. 

Younger: He'd teach you how to read and write, then try to get you into college as you get older. Pony wants the best for you. He would never let you walk home alone or anything. 

***

Steve

Older: You'd stick up for him whenever your father was being a jerk. Whenever Steve got kicked out of home, you'd always make sure he was okay and had somewhere to go. You wash his clothes and bandage him up whenever he would fight.

Younger: Steve would teach you all his knowledge about the town and the people in it. He'd tell you who to stay away from, and who you can trust. He'd teach you how to drive and the basics of owning a car. 

***

Two-bit

Older: You would have to pay his bail whenever he would get into trouble or even talk people out of fighting him when he is drunk. You beg him to stop drinking, and stealing stuff. He ignores you but then pickpockets stuff you want but can't afford. 

Younger: You keep him sell stolen goods. He doesn't let you go out with him while he drinks but always brings you home small toys or things you like. You send Sunday mornings watching cartoons in front of the television with cereal even when he's hungover. 

***

Darry

Older: You take over the family responsibilities when your parents died and let Darry go to college. He helps out whenever he can with bills and stuff, but you want him to live up to his potential. 

Younger: You'd see him more like a father than an older brother. He'd let you get away with a lot but also be strict on certain things such as school. Darry would be wildly overprotective of you and forbid places around town where there is danger. 

***

Sodapop

Older: You would ring Sandy up on the phone and give her a piece of your mind after she left him. Even though you both argued a bunch, you still stuck up for each other. I think you'd be the closest out of all. 

Younger: Being both the middle child you tend to argue a bunch, but always be on each other sides. He'd get mad whenever you'd have a crush on Steve. 

***

Johnny

Older: You would rent a house so that he didn't have to deal with your parents. The two of you would work together to make a better life for yourselves. You would read to him a lot, and take long walks, promising him things take time but will get better. 

Younger: Johnny would protect you from everything. He would give you his jacket whenever you were cold and find a way to get the two of you out of your parents abusive household. He practically raised you even though he is only a few years older.