1. Bill was a formal war officer known for burning down entire towns to capture outlaws. John and Lillie were both survivors of one of these towns.
2. It seems a bit cliche, I've heard stories like this before. Try this, John used to look up to bill, until he set his parents on fire and forced him to watch. Bill did the same to Lillie, John adopts her because he sees an image of himself in her.
3. I'm thinking, John used to think Bill was some sort of hero until he fell victim to his cruel methods of "regulating the law"
4. John grew older not expecting for justice to be served. One day, upon finding Lillie, he decides the only way for justice to ever be served is for individuals like himself to take justice into their own hands.
5.1. Lillie's story is that her town was gunned down by Bill and his men after wrongfully thinking there was a bounty on their heads. Bill forgets about Lillie and leaves her in the desert to die. John finds her and saves her life.
5.2. Lillie's parents are held hostage to be sold off to the sheriff. The sheriff didn't plan on paying the ransom because he doesn't believe in paying off criminals. Lillie tries to save them on her own, and ends up getting them killed. John hears about how she was planning this, and shows up just in time to save her before they can kill her.
6. Cassius is John's cousin. They grew up both together, and Cassius was adopted by Bill, whom he strongly admires for his ruthless crimes. So Bill is much older then John and Cassius, possibly by ten years.