One common theme could be the exploration of unspoken or alternative relationships between the characters. Since the original series has complex characters, in gay fanfiction, it might be about re - imagining their emotional bonds in a romantic or more intimate way.
I'm not sure about specific 'A Series of Unfortunate Events' gay fanfiction. But you can try searching on fanfiction websites like Archive of Our Own. There might be some creative works there that re - imagine the relationships in the story in a different way.
No. 'A Series of Unfortunate Events' is a story mainly aimed at a general audience, including children. Creating fanfic with sexual content, especially gay sex content which is not in line with the original family - friendly nature of the work, is inappropriate and violates the spirit of the original story.
I haven't come across many popular ones. Fanfiction is a diverse field, but specific themes like this might not be as mainstream. You might have to search on dedicated fanfic platforms or communities to get more accurate results.
There are several ethical problems. Firstly, it disrespects the original creator's intention. The original work was created with a certain vision in mind, and adding such sexual content goes against that. Secondly, it can make the fan community seem inappropriate. Fanfic should be a positive extension of the original work, not something that includes sexually explicit and inappropriate content that can make others uncomfortable or offended.
Another theme is mystery. The original series is full of mysteries, and fanfiction continues this trend. It could be a mystery about a new character, a hidden place, or a secret code. For example, some fanfictions might introduce a mysterious figure who seems to know more about the Baudelaire parents than the orphans do.
Definitely not real. 'A Series of Unfortunate Events' is a work of fiction that takes readers on an imaginative and often quirky journey. It's not based on actual events or people.