Ok. Bullet isn't setup for partnership business. It's a old type of company. Then the other company is a sole trader company. As a sole trader you are the 'company' the money in/out is yours. So the concept of two legally different doesn't really exists with sole-traders. Normally I'd say just use the different invoice templates for each company you can't have separate bullet accounts as that means you've separate companies. But seeing as your in a partnership that's VAT Reg and a sole trader that isn't you'll need two separate accounts with two separate logins.