How and why were the boys named?

Ponyboy: From a young age Sodapop loved horses, even so much that he asked for one instead of a sibling. He was upset when his parents brought him a baby, so they decided to call him Ponyboy.

Sodapop: Like most people Soda's parents knew that the delicious taste of this drink was too good to pass up the opportunity of naming their second son as.  During the pregnancy Mrs. Curtis would crave it so much that they decided to name him Soda. 

Dallas: To be honest his parents were on so much drugs at the time that they got the name Garrett and the city of Dallas mixed up when signing the papers. Never could be bothered to change it, so Dallas was his name. 

Two-bit: Although he is born as Keith, his nickname came from the meaning of insignificant and cheap, which his fourth grade teacher put on his report card. From then on he'd be known as that. 

Johnny: His mother was obsessed with Johnny Cash as a young girl. She knew she'd call her first child Johnny no matter if it was a girl or boy. 

Steve: His parents had a big book of baby names, instead of picking themselves, they closed their eyes and pointed one out. Steve was his name from then on. 

Darry: Mr. Curtis loved milk... I mean he knows the importance... some guys his age didn't... they forgot about it... It's good he'd say... natural... its uh...satisfying... he loved when its ice cold... he couldn't beat it and decided to...drink milk for good. He wanted his first son to take on that legacy.