I'm not really sure what you mean by 'kanao comics hentai'. It might refer to some adult-oriented or inappropriate content related to a particular character.
In the manga, Tanjiro and Kanao don't end up getting married. The story focuses more on their battles and character development rather than romantic pairings.
Nezuko is initially 12 years old in the manga. As the story unfolds, her age doesn't change significantly in a traditional sense, but her character development is quite remarkable.