Well, BIMI doesn't operate at the Marketo-partition/DB level. A default BIMI record should be published at the Organizational Domain, allowing it to be inherited by all subdomains. However, if a BIMI record is found at that subdomain, the mailbox provider can use it (even if it differs from the BIMI record published at the Organizational Domain).
Also, as a general rule, you will need one VMC per logo. Having a VMC for your organizational domain will cover subdomains, and with an added feature even different domains. In case you have different logos, more than one VMC is needed.
So if you've different sending domains/sub-domains for different brands, then I suppose you'd be able to set a relevant BIMI record for each and have the client retrieve the correct logo based on the sending domain, or as in your case set the BIMI record for the sending domain of the brand you wish to.