What had happened in the Sappleton family as narrated by the niece?

The narration by the girl (niece) about the Sappleton family was connected to the tragedy which happened just three years ago. The niece described how through the window, three years ago, Mrs. Sappleton’s husband and her two younger brothers went off for their day’s shooting but never came back. While crossing the moor to their favourite shooting ground, all three of them were engulfed in a treacherous piece of bog, even their bodies were not recovered. The niece further stated that her aunt fascinated their entry through the window so it was always kept open every evening till it was dusk. Her aunt always awaited their return.