- You have to decide how to appear to others: The Madison's vs Dan Madison and Ann Madison
How you describe your business relationship should be consistent. It will likely also bring the kind of conversations people have when they're going to get married and are deciding on hyphenation or not, etc. Being sensitive to each others needs for a clear identity is key to making this part of working together work.
How you word this partnership is also a huge cue to your employees, vendors and customers on how to treat you. If every time the phone rings and they ask for Dan and if he's not in they ask for Ann, it's gonna get old. Chances are, you're in very different roles and are not interchangeable.
It's funny the assumptions that come just with people who are in business together who have the same last name but are not spouses or not related at all! So, assumptions are being all the time. It's up to you to set the boundaries for yourself AND others.