Hello,
The HikaMarket category edition, using an admin account, could allow to create categories under the "brand category".
But there is a restriction in HikaMarket code so only "product" and "vendor" categories can be edited ; and only "product" categories can be created.
It requires some development (and test) but the feature is possible.
The only condition is that only the main vendor would be able to edit or create brands (which would be always your case since you're using the "front-edition" version of HikaMarket)
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.