Everyone has siblings including him.
No, they don't. 
Siblings are brothers and sisters, it's not the same as your next of kin. Your wife/husband and children are not considered siblings. So if he does not want to inherit, who will be the owner of the forum 
Whoever deserves it the most due to his contributions to the forum and the work done in the background. The stuff we can't see from posts and sharing on-forum content.