- Thursday Caliban
- Miranda Caliban (†?)
- Olivia Caliban †
- Friday Caliban (†?)
- N (possible)
- Monday (possible)
It is possible that the people in Thursday's family are named after days of the week, following each other; Friday, his daughter, is named for the weekday after his. This could mean that Count Olaf's associate, Monday, is a member of the family.
- Snicket Clan
- It is theorized that Miranda and Olivia are sisters, and the M and the O on the Snicket Clan tree from Lemony Snicket: The Unauthorized Autobiography. This would make them the daughters of F. Snicket, the granddaughters of Chas. Snicket, and the sisters of N.
- This theory could be possible in the book canon; it is probably untrue in the Netflix canon, as this would make them first cousins of the Snicket siblings, and in the Netflix series, Jacques Snicket and Olivia Caliban have a romantic relationship.
- Widdershins Family
- Miranda Caliban is Mrs. Widdershins, and she retreated to the island, leaving Widdershins to claim she was dead. This would make Fernald and Fiona siblings or half-siblings of Friday Caliban, depending on the identity of Thursday; many theorists believe that Thursday may be Widdershins himself, as Widdershins's first name and Thursday's surname are not revealed.
- Both Miranda and Widdershins use the excuse of a "manatee accident" to explain the disappearance of their partner.
- Fernald, Fiona and Friday have alliterative names, presenting a pattern. Another fact supporting this theory is that most siblings in the series come in groups of three, and even on the rare occasions that only two siblings are known of, the existence of a third sibling is usually hinted at (such as the White-Faced Women). The only known siblings in groups of two (aside from Fiona and Fernald) are from All the Wrong Questions: Pip and Squeak Bellerophon, Kellar and Lizzie Haines, Zada and Zora, and Tatiana and Treacle Cozy.
- Evidence against this theory could be that Kit Snicket believes Friday's father and Miranda's husband, Thursday, is alive and well, and mentions dining with him the day before meeting the Baudelaires. The day before meeting the Baudelaires, Captain Widdershins was with them on his submarine, and by the time Kit was discussing Thursday, Kit believed the Captain to be either deceased or in mortal peril due to the crash of the Queequeg and arrival of the Great Unknown.
- The name Caliban comes from a character of the same name in William Shakespeare's The Tempest.
- The play concerns a group of people stranded on a deserted island, much like Miranda, Friday and the other colonists of The Island.
- In The Tempest, Caliban is a monstrous character who serves as the primary antagonist; Shakespeare seems to have created the name specifically for this character, and comes from the Spanish word canibal.
- Miranda's name is also taken from this play: In The Tempest, Miranda is a girl who was raised on the island by her father, ignorant of the fact her father is an exiled duke and she should rightfully be part of the royal family of Milan. This could be considered a parallel to Friday's ignorance of the survival of her father and her mother's past on the mainland.
- Several other islanders are also named after characters from the play- Alonso, Ariel and Ferdinand. Alonso also mentions a man in his past named Gonzalo, and Olaf uses the name Stephano for a disguise.
- Interestingly, Olivia's first name is also shared with a prominent Shakespearean character, though this time from Twelfth Night instead of The Tempest.