Actions are the main way we get a sense for the minor characters in the story, and they say a lot. The kids say nasty things to their grandmother and to strangers, and also throw a spectacular tantrum to make their Bailey take them to the plantation house. Bailey loses his temper a lot and appears to be fond of clenching his jaw and saying "shut up." Bailey's wife says nothing and does nothing except that she attends to the baby. And then, of course, there are the Misfit's accomplices, who have good fun killing the family in the woods. The primary mode of learning about the characters is through their actions, because there's not much depth to the people depicted.
The Misfit and the grandmother are more complicated, because they do a lot of talking and are given more depth. The challenge is to find out what their actions mean. Some of the grandmother's actions early in the story appear to establish her as a manipulator. Once she's up against The Misfit, however, it's not clear what motivates her actions. Is she a conniving manipulator or a poor older woman on the verge of a breakdown? We know The Misfit does a lot of bad things – both from what he tells us, and from what he actually does in the story – but the big question about him is why he does them. It's our job to figure out his motivation from what he says and thinks.
The grandmother's roots in old Southern "gentleman" culture come out in her carefully-chosen clothing. In addition, her superficial nature is also manifest in her clothing choices. We're thinking specifically of that outfit with white cotton gloves, lace-trimmed collars and cuffs and the "purple spray of cloth violets" at her neckline, which is described over the course of an entire paragraph (12). She cares about looking like a "lady."
The grandmother's clothing provides a stark contrast to The Misfit and his accomplices, who are wearing mismatched and haphazard clothes. Their clothing reflects their particular set of circumstances: far from being good gentlemen, they're trying to hide from the law and actually got rid of their old clothes. That The Misfit doesn't have a shirt may add a sense either of directness or vulnerability to his character. (Notice that the grandmother perhaps picks up on this.) He's not concerned with appearances. Finally we have Bailey with his ridiculous parrot shirt. Maybe the point is to just make him more ridiculous, in the way only a badly dressed, modern middle-class dad on vacation can be.
The family's dysfunctions are revealing. How each family member interacts (or doesn't) with the rest of the family is the main way we get a sense of these characters. Recall the kids' bad behavior and disrespect for their elders, the mother's fixation on the baby, and Bailey's unsuccessful attempts to stay in charge as the "dad." On the other hand, the family is still together, and apparently manages to go on family vacations. Compare that to The Misfit's family situation: he (probably) killed his dad (although he won't admit to it). That's some real dysfunction to consider.
O'Connor's fond of giving her characters speech that reflects their age, social class, or region (almost always Southern). The kids constantly say exaggerated things that sound childish – like "We've had an ACCIDENT" in all caps, or June Star's "wouldn't do that for a million bucks." And of course The Misfit has a pronounced down-home Southern (and lower class) accent, filled with "oncet" and "twict," "would of" instead of "would have," "Yes'm," and "nome." This contrasts quite sharply with the grandmother's standard speech.
This is most relevant to the two major characters, the grandmother and The Misfit. The grandmother's nostalgia for the old days, her emphasis on manners, and her equation of "good blood" with "goodness" tell us a lot about her. The Misfit's character gets most of its meat – and its mystery – from what he says about religion and his understanding of good and evil.