Creating the display to get only the categories you are looking for based on the particular brand will be tricky to say the least. I think that the one of the easiest ways to do this would be to add in some custom code that would look for the categories that you don't want to show within the repeat region and if that category is found just skip that and move onto the next one. If you can post back with the page in question and the names or id's of the categories I should be able to make an example of what this code may look like for you.
