One license can be applied in a multisite installation. The only requirement is that the sub-domains and sub-folders of this site should belong to one single end product.
Create a domain (website.com), which becomes your primary (parent) domain. Then attach subdomains (sub-domain.website.com) or subfolders (website.com/sub-domain) and use the same license key to register the Companion instances on the primary domain.
Or use WordPress Multisite feature to create Consulting theme instances and register them using one license key.