The family, specifically the grandmother, are alazons (those who think they are better than they really are); they are essentialists (those who believe in a perfectible human nature); they are lost on the road (spiritually and physically); they are "once saved, always saved" hypocrites ("wingless chickens" who think they are going to heaven and, therefore, do not take responsibility for themselves or others).
"A Good Man is Hard to Find" (1955) tells the story of a family en route from Tennessee to Florida for vacation. Through a series of the mishaps by the grandmother and her cat, the family car wrecks near some woods in Florida. Two witnesses from a following car stop to aid the family, all of whom are relatively unscathed. The grandmother identifies one of the witnesses as The Misfit, a mass murderer on the loose.
Her admission is a death sentence for the family. The Misfit's accomplice takes the family into the woods and shoots them. The grandmother tries to save herself by pleading to the Misfit, "You've got good blood! I know you wouldn't shoot a lady! I know you come from nice people! Pray! Jesus, you ought not to shoot a lady. I'll give you all the money I've got!"
The Misfit responds, "Jesus was the only One that ever raised the dead and He shouldn't have done it. He shown everything off balance. If He did what He said, then it's nothing for you to do but thow away everything and follow Him, and if He didn't, then it's nothing for you to do but enjoy the few minutes you got left the best way you can--by killing somebody or burning down his house or doing some other meanness to him. No pleasure but meanness."
Just before it is her turn to be shot, the grandmother says, "Why you're one of my babies. You're one of my own children!" She touches the Misfit on the shoulder, and he springs back "as if a snake had bitten him and [shoots] her three times through the chest."
The Misfit tells his accomplice to throw the grandmother into the woods with the others, adding: "She would have bee a good woman if it had been somebody there to shoot her every minute of her life."
The family, namely the grandmother, are spiritual idealists. The grandmother's idealist arguments "you’re a good boy" and "you wouldn’t shoot a lady" are empty attempts to verify a truth for the situation that she wants to be affirmed in him, but that which she knows to be false. She has had a history of validating herself though the eyes of others, and O'Connor uses the Misfit's grotesqueness as a means of showing her inauthenticity.
I see the grandmother in a more negative way than the above, and, therefore, see her son as more miserable.
The grandmother is impossible to please, a bully, ignorant, stubborn, arrogant, self-important, self-righteous, and makes her son absolutely miserable. He is nit-picked and bullied, and he is even less of an attractive character than he might otherwise be for letting it happen and not standing up to his bitty of a mother.
The ending isn't made more horrific because the family is normal. The grandma doesn't deserve to be shot, of course, but she deserves what The Misfit recommends: someone holding a gun to her head every minute of every day--that's the only thing, says The Misfit, that could have made her a good woman, the only thing that could have convinced her that she wasn't the only person in the world that mattered, and she wasn't smarter and holier than every other person in the world.
Imagine if The Misfit threatens the family and the grandmother, but instead of actually killing them only ties them up and gags them. Wouldn't you have cheered? The grandmother could have used a gag in her mouth.
The family that is portrayed seems like any other normal family that has all of its own annoying quirks. The grandmother is whiney, sneaky and judgmental; her son is appropriately annoyed. The kids act like normal kids, complaining and making funny comments on the trip. They even have the family pet in the car, adding to the confusion and chaos. The family seems like any normal, weird, funny family with issues.
Because they are so normal, it makes them more relatable and understandable. We can read our own families into them and connect with them. That makes the ending even more traumatic and shocking; the fact that they die is tragic and horrific. We even feel bad for the grandmother, who throughout the entire story had been completely irritating. I hope that those thoughts help a bit; good luck!