Character Analysis
There's a whole list of these folks. You've got Amos and Louisa Ames with their cousin Minnie in Homecoming. In The Hunted, there's Josiah and Emma Borden, Dr. Joseph Blake, and the Reverend Everett Hills and his nameless wife. And, finally, you've got Amos Ames, Ira Mackel, Joe Silva, and Abner Small in The Haunted. Seth makes an appearance as a part of the chorus proper in the first and final plays in the trilogy.
The townsfolk's gossip both comments upon what's just happened and lets us know some valuable info that we wouldn't otherwise have picked up. Along with Seth, they function like the chorus in any Greek tragedy. O'Neill is pretty explicit about this.
It's important to keep in mind that the Ameses and their cousin symbolize the townsfolk's love of spreading gossip. The group we meet in The Hunted represent the hoity-toity rich folks that have more in common with the Mannons. Seth and his drinking buddies in The Haunted represent salt-of-the-earth working folks. O'Neill wants the chorus to include a bunch of people that represent specific types of people you might meet in any New England community—maybe even in any community anywhere. They each have different experiences of the Mannons and can bring those unique perspectives to bear when they add their commentary.