Well, comparing the two, it depends on various factors. But if we look at their overall showings in the manga, Hisoka seems to have the upper hand with his versatility and bold fighting style. Illumi is no slouch either, but Hisoka just seems to have that extra edge.
I think Hisoka is stronger. His fighting skills and strategies seem more unpredictable and powerful in the manga.
No, they aren't. There's no such plot or indication in the manga.
No, they aren't. There's no such plotline in the manga.
No, they aren't. There's no indication of them being married in the manga.
No, they aren't. There's no such plot or development in the manga.
I'd bet on Hisoka. His fighting style and ability to adapt in tough situations give him an edge over Illumi in my opinion.
Definitely not. Hisoka and Illumi have a complex relationship in the manga, but marriage isn't part of it. Their interactions are focused on other aspects of the story.
No, they didn't. There's no such plot in the manga.
Hisoka and Illumi's relationship in the manga is a blend of rivalry and a sort of strange alliance. They don't always see eye to eye, but they both recognize each other's skills and use that to their advantage in various situations.
It's a complex and somewhat ambiguous one. They have interactions that are full of intrigue and mystery.
In Hisoka x Illumi yaoi fanfictions, the attraction between them could be based on mutual respect for each other's power. Hisoka is always seeking strong opponents, and Illumi is a very powerful assassin. Their interactions in the original work provide a rich source of material for fanfiction writers to develop romantic or at least deeply emotional relationships between them.