It's a complex and somewhat ambiguous one. They have interactions that are full of intrigue and mystery.
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.
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 think Hisoka is stronger. His fighting skills and strategies seem more unpredictable and powerful in the manga.
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 connection in the manga is a bit mysterious. They both are powerful and have their own goals. They might collaborate for mutual benefit or have secret motives against one another. It's hard to predict their actions.
I'd bet on Hisoka. His fighting style and ability to adapt in tough situations give him an edge over Illumi in my opinion.