By sharing a "Customer Realm" between two stores you can allow customers to log into multiple websites with one account. Delivery addresses and other account information are then accessible across all stores and a single password is required for all associated sites.
The customer must accept Terms & Conditions per store. This allows you to ensure data sharing between and sub brands, labels, or artists is handled in a clean, clean manner.
To set up shared Customer Realms contact the Ochre team.