Where are the quagmire children in book The Ersatz Elevator?

The Quagmire children, Isadora, Duncan, and Quigley, are not mentioned in Lemony Snicket's "The Ersatz Elevator". This is because they disappeared in the previous book, "The Ersatz Elevator".

The Baudelaires are left to believe that their siblings are with their guardians, Count Olaf, but it is never explicitly stated what happened to the Quagmires. Their fate remains a mystery throughout the series, adding to the overall unsettling tone of the books.