A SCH C is used to report the business income/expenses of a single owner business. Period. Doesn't matter that it's part of a joint return. But only one of the joint tax filers can be the owner of the business. There's also nothing wrong with one joint filer being the owner, and the other joint filer being an employee of that business whose pay is reported to them by the business on a W-2. (Helps increase the amount the W-2 employee spouse can make to a retirement account.)
