These three are Mr. and Mrs. Shortley's children. Annie Maude is fifteen and Sarah Mae is seventeen. Mrs. Shortley thinks that Sledgewig is better looking than they are. Her son H.C. is twenty. Apparently he looks like Mrs. Shortley and she thinks he's better looking than Rudolph. H.C. is studying to be a preacher. We never meet H.C. and we only hear about the girls until the morning of the family's departure from the farm. The bizarre thing is that we don't hear anything about them after this. Mr. Shortley returns to the farm alone.
One reason we don't know what happened to them is because Mrs. McIntyre doesn't ask, which further highlights her callousness. But, certainly O'Connor could have given us the information in another way. By omitting it she again encourages us to use our imaginations. Whatever the case, we can suspect that they too have become displaced persons, and that their lives are pretty rough.