Darry affects Ponyboy by believing him because he makes him stay in school. Darry doesn't want Ponyboy to drop out and make the same mistake he and Soda did. Also, Darry is teaching Ponyboy to be responsible and to stand up for yourself. And when Darry and Ponyboy decided to stop fighting that affected Ponyboy by getting closer/make it easier for Ponyboy to come home every day.
The Park affected Ponyboy by making him and Johnny run away from killing Bob. And it made Ponyboy tougher and he was able to stand up to the Socs after the Socs saw Johnny kill Bob and now they are scared of Ponyboy and the other greasers. It also made Ponyboy bleach and cut his hair and Johnny cut his hair so they could hide from the police. Ponyboy became more responsible after the park incident and now makes him stand up for himself to the Socs.
Johnnys death affected Ponyboy by making him tougher. Johnnys death also makes Ponyboy not forget him. Neither Dally or Ponyboy took Johnny's death good, all the greasers lost a friend that day but Dally and Ponyboy lost family. What I mean by that is they were 2 that were more close to Johnny than the other greasers.