An example of situational irony in the excerpt is:
“‘I hope you don’t mind the open window,’ said Mrs. Sappleton briskly; ‘my husband and brothers will be home directly from shooting, and they always come in this way.’”
This is ironic because, while Mrs. Sappleton believes she is waiting for her husband and brothers to return from shooting, the audience (and Framton) knows that they died three years ago and that the open window symbolizes their absence and the aunt's delusion. The cheerful expectation of their return contrasts sharply with the grim reality of their fate.