Why are there random brands showing up in my footer or website sitemap?

Every BigCommerce store comes with some sample products, categories and brands.

To delete the sample brands, go to Products > Brands. Click the checkbox to the left of the brands you want to delete and then click the trash can icon at the top of the page. Brand deletion is instant so no need to save.

Note that deleting a brand does not delete any products that are assigned to that brand. It simply disassociates that brand from the products.