I'm not aware of any supported way to create Request Types in this way; i think it will be a manual process.
Depending on it if works for you, it might be easier to use a Custom Field for Brand that is "required" to answer, e.g.
-- Request Type
-- Detail Type A
-- Detail Type B
-- Detail Type C
but then have a custom field (drop-down) for Brand with options (Brand A, Brand B, Brand C)
Thanks, that is what I was afraid of.
I offered that as an option too for Brands, but the powers that be didn't like that option. They wanted them to think Brand from the very beginning.