I may be wrong, but I don't think he has a registration problem. If he was not registered, he would go from a "search results" page to a "please join up" page and would never see anything to merge.
Unless it is one of Ancestry free databases.
You can tell if you are registered if you can see your member name in the upper right of the Home page, and probably many other pages, as well.
If he/you are having registration problems, the best thing to do is to call ancestry. They can reset your registration.
Also, keep in mind that you cannot be signed up to ancestry with more than two computers. You can have more than one tab on one computer open to mulitiple ancestry pages, and also more than one browser, including the Web Search window in FTM open to multiple ancestry pages - but you can't have two separate computers signed into ancestry. For example, if your wife was working in the same member name on a different computer, that might be the cause of this problem, as well.