how is boo raldy,tom robinson and mayella set as mocking birds

Boo is deemed a mockingbird because he was unjustly incarcerated by his father for what most would consider a prank.

"One night, in an excessive spurt of high spirits, the boys backed around the square in a borrowed flivver, resisted arrest by Maycomb’s ancient beadle, Mr. Conner, and locked him in the courthouse outhouse. The town decided something had to be done; Mr. Conner said he knew who each and every one of them was, and he was bound and determined they wouldn’t get away with it, so the boys came before the probate judge on charges of disorderly conduct, disturbing the peace, assault and battery, and using abusive and profane language in the presence and hearing of a female."

Rather than go to the Industrial School, Boo's father arranged for his son to be remanded into his care. He locked him away and never allowed him out. The rest of the boys;

"The other boys attended the industrial school and received the best secondary education to be had in the state; one of them eventually worked his way through engineering school at Auburn. The doors of the Radley house were closed on weekdays as well as Sundays, and Mr. Radley’s boy was not seen again for fifteen years."

Tom Robinson has never hurt anyone. In fact, he went out of his way to be a helpful, courteous member of the community. He is unjustly accused and unjustly condemned. He was an innocent.

Mayella is a mockingbird because her youthful innocence was taken away by the physical and emotional abuse heaped upon her by her father. Sadly, it is also her lies that put Tom Robinson is jail. The destruction of her innocence resulted in the death of another human being.