Does divorce occur for a scrupulous man who doubted that he swore by divorce not to enter into a partnership with his uncle if he resumed the partnership, and is it permissible for him to have his mother partner with him to avoid that?

Divorce does not occur by mere intention, self-talk, or doubt about uttering it. Therefore, as long as you are not certain that you uttered the oath of divorce, do not pay attention to doubt, proceed with your permissible dealings with the man, and seek Allah's help to get rid of obsessive whispers.