The documents we provide don't support the option to exclude someone from becoming a Guardian, but this is because it's not exactly necessary to do so.
The good news is you can designate who you do want to be Guardian, and in almost every case, your designation will be what happens.
In rare situations, it may not be possible for your designated Guardian to fill that role (For example: They've passed.) In that case, a court may have to decide who the Guardian should be. That said, the court will always consider what's best for the child when appointing a Guardian.
The court makes a determination based on its own investigation. This means the court will discover any reasons that a particular person should not be Guardian, and they will not be appointed.