Thanks for reaching out on the Community, @john999 

Each subscription under the same email address will be linked to a single Intuit user ID. This means the sign-in can't be separated as changing the email/username used to sign in will update across each company. 

As a workaround, you can add yourself as a new user to one company (with a different email address). Once added, delete the user with your original email. Please note, if you're the Primary admin of the company, you'll need to transfer the PA role to your new user before deleting.