As shown from the Snicket family tree, G. is the child of D. Snicket and the (presumably elder, seeing as their name is listed first both on the tree and alphabetically) sibling of H and I. They are the grandchild of Chas. Snicket, the grand-nibling of A and B, the nibling of E and F, and the cousin of Jacques, Kit, Lemony, M, N and O. This would make Beatrice Baudelaire II their first cousin, once removed.
G is theorized to be Gregor Anwhistle, which would make his sibling I Ike Anwhistle. As many VFD families are interconnected, it would make sense that the Snickets and Anwhistles were related, and if D. was the parent of Gregor Anwhistle, it would make sense for them to be his mother, who was described by Ike's wife Josephine as having one eyebrow and one ear. H's identity would still be a mystery, though they are occasionally theorized to be Hector.
If G is Gregor, that would make them the second cousin of the Baudelaire family, and would mean that he is deceased.
|A. Snicket||B. Snicket||Chas. Snicket|
|D. Snicket||E. Snicket †||Jacob Snicket †||F. Snicket|
|G. Snicket||H. Snicket||I. Snicket||Jacques Snicket †||Kit Snicket †||Lemony Snicket||M. Snicket||N. Snicket||O. Snicket|
|Beatrice Baudelaire II|
|A Series of Unfortunate Events (Books)|
|1. The Bad Beginning (1999):||Absent||7. The Vile Village (2001):||Absent|
|2. The Reptile Room (1999):||Absent||8. The Hostile Hospital (2001):||Absent|
|3. The Wide Window (2000):||Absent||9. The Carnivorous Carnival (2002):||Absent|
|4. The Miserable Mill (2000):||Absent||10. The Slippery Slope (2003):||Absent|
|5. The Austere Academy (2000):||Absent||11. The Grim Grotto (2004):||Absent|
|6. The Ersatz Elevator (2001):||Absent||12. The Penultimate Peril (2005):||Absent|
|13. The End (2006):||Absent|
|All the Wrong Questions|
|Who Could That Be at This Hour? (2012):||Absent||Shouldn't You Be in School? (2014):||Absent|
|When Did You See Her Last? (2013):||Absent||Why Is This Night Different from All Other Nights? (2015):||Absent|
|File Under: 13 Suspicious Incidents (2014):||Absent|
|Other Snicket Books|
|Lemony Snicket: The Unauthorized Autobiography (2002):||Appears|
|The Dismal Dinner (2004):||Absent|
|The Beatrice Letters (2006):||Absent|
|The Hero of the Story (2017):||Absent|