I'm fairly new here, I don't know whether my reply will be of much help, but it might help your question gain visibility in the forum for others to reply.
Although we commonly use admin/administrator even in place of owner of the website, these are two distinct levels. Several people can be admin to a website, there can only be one owner. The owner has full control and access to the website, and can make someone an admin and (I suppose, though I haven't tested it) take administrator privileges away. If you are the owner (or someone else who has access to the website is), it should be no problem to revoke administrator privileges. I fear, though, in your case either you late brother or his late wife was the owner. In this case, I believe you should contact TribalPages support