Nick here from Shopify. Really good question!
In this case, you wouldn't be able to have two accounts under one log in, but when you have multiple Shopify stores associated with the same email address, you can navigate between them after you log in to your Shopify admin. You can see an example of how this would look for a brand with stores running in multiple countries below:
In this case it would act, look and feel like a stand alone brand and navigate between the stores easily as long as they have a united email address. You can see the full help and information guide Shopify has for this here.
Would this work for you, do you think?
Let me know, Nick