Explain the title of the play. Who are "all my sons"?

Yes, you're on the right track. "All MY Sons," are the pilots who died for their country. The pilots Joe Keller was responsible for, and the son he raised. The title is significant because it isn't until Joe reads a letter from his dead son in which he finally comes to understand that the dead men he denied responsibility for were in fact his responsibility. The title signifies that we are responsible for far more in this world than those things inside our immediate circle...... that what we do can impact a far larger group than we initially believe.

"All My Sons" - all of Joe's sons. He had two sons: Larry and Chris. Larry had committed suicide in the war after hearing about The Case, in which Joe's factory had shipped defective parts that killed 21 pilots. Larry is very idealistic and he identified with the soldiers, he couldn't take the thought his father was a murderer so he committed suicide. The title comes to express the idea that Joe shouldn't be thinking only of Larry as HIS dead son - but of all the 21 pilots who dies (because of the parts his factory has shipped). All my sons - Larry + 21 dead pilots.