Sire.....There are folk in this thread who are complicating matters with issues that cannot arise until after you have died.
Wills can be disputed and Court cases do arise over them. However, I don't think you wanted to consider disputes that could arise. You wanted to know who is legally entitled to all money remaining in your joint account.
You have said.../" All I wanted was a simple answer in words of one syllable that I could understand; not a lot of legal jargon."/
Accordingly, I suggest you look no further than what was said by Aunt PG; in the very first response in this thread. /" On your death the contents of your joint account would automatically go to the named person with you on the account."/
Hans.