"Having it all rolled into one amplifies the complexities," he said.
Couples who own businesses can be so caught up in each other that they run the risk of isolating employees, he said.
"The familiarity and comfort in their marital relationship oftentimes is not the same kind of way people would talk to one another in a professional relationship," he said.
And that can be uncomfortable for staff or customers, Duening said.
Also, couples in business can have an "unspoken understanding between one another" and use passive communication that shuts out other employees.
Bringing relationship issues to the workplace can be detrimental, Duening said.
"It sometimes spills over because they have difficulties separating the marital issues from the business issues, and it becomes awkward," he said.
While couples who don't work together can vent to one another about job concerns, a husband and wife who are in business may not be able to be honest with each other regarding workplace matters, he said.
"Especially if it's a tense situation around performance, you don't notice all the implications for the team," Duening said.
"So it has to be carefully managed; you have to demonstrate transparency and forthrightly address issues."