Can some please answer these crazy questions? Spoilers

After his wife died, the father turned to drugs. I'm guessing that's why he went to jail the first time. Or hurting his son. Probably both. As far as the rest, drug-related things maybe, including but not limited to theft. He WAS a thief.
There was a crash, and that's how the mother died, but that's NOT how the guy's leg was hurt. His father, drugged out of his mind, literally threw him down the stairs. THAT is what crippled him, not the wreck in which his mother died.
Here's the dialogue explaining it:

Jason Lair: No, he sent us here so I could forgive you. That's all my post-it said was, "Forgive him." What am I forgiving you for, Turner? Huh? What am I forgiving you for?
Turner Lair: What happened here... there's no forgiveness.
Jason Lair: What happened on the stairway, Turner? Just tell me, what happened on the stairway?
Turner Lair: You were not in the car.
Jason Lair: What?
Turner Lair: With your mother. You were never in a car accident.
Jason Lair: What'd you do? Did you drop me? Is that it? You get ƒucked up? You get ƒucked up and you dropped me?
Turner Lair: ƒucked up? I WAS GONE!
Jason Lair: Just... say it! Say it! Say it! You dropped me! Say it.
Turner Lair: No... no. No! NO! Nobody dropped you! GET IT? I threw you, kid. I threw my boy... I threw my boy.

"Pay no attention to the man in the trunk."