Nobody seems to have an answer for you and your (IMHO) unusual business scheme about invoicing each other.You can have all 3 businesses in one A/R and one A/P account in Quicken, or you can use separate ones. What makes an invoice a "Company A - issued Invoice" vs. B or C is the setting of the "Business tag" field in the New Customer Invoice data entry form. You need to set this field individually for each invoice you write. There's no setting you can specify to make "A/R account A" use default values for Company A and Business Bank Account A. Ditto for B and C.If you are a sole proprietor and all three businesses' Income and Expenses are reported in your Personal Income Tax Return plus 3 Schedule C forms ... I'd discuss this scheme with a qualified tax accountant or tax attorney, to verify if that's even allowed or necessary.
Do you have the companies setup in separate data files or all in the same file?