According to the narrator, the Griersons "held themselves a little too high for what they really were." They considered themselves to be a higher class than most of the other people in the town. As a result, there was not a young man in town who was "quite good enough" for Emily. For that reason, we can't say how Mr. Grierson treated the men who wanted to date her, because there weren't any until Homer Barron came to town. We know this because the narrator tells us: "So when she got to be thirty and was still single, we were not pleased exactly, but vindicated; even with insanity in the family she wouldn't have turned down all of her chances if they had really materialized."

In "A Rose for Emily," how did Emily's father treat her suitors?

In "A Rose for Emily" by William Faulkner, Emily's father, Mr. Grierson, is only mentioned briefly at the start of the story. The narrator informs us that the Griersons are an aristocratic family.  Emily's mother is dead, and Emily is separated from the town and social contact by her father. Mr. Grierson chases off any male who wants to court Emily because he doesn't believe any of them are "good enough." 

None of the young men were quite good enough for Miss Emily and such. We had long thought of them as a tableau, Miss Emily a slender figure in white in the background, her father a spraddled silhouette in the foreground, his back to her and clutching a horsewhip, the two of them framed by the back-flung front door.

The story doesn't specifically state how the men were treated who wanted to court Emily. The reader has to infer what probably happened, based on the tableau painted by the author. In the image, the reader sees Emily's father "clutching" a horsewhip.  By reading between the lines, the image suggests the father chased them off, aggressively protecting his daughter.