How to navigate the ups and downs of starting a business with your spouse, sibling, or best friend - from 5 founders who have done it

• It's common for cofounders to have an established relationship before they start a company together.
• Running a business with your spouse, best friend, or family comes with its own challenges.
• Business Insider talked with five cofounders who shared the lessons they've learned in marriage and friendship, and how they make the most of their strengths to work together.
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It's common for cofounders to have an established relationship before they start a company together.

Business Insider has interviewed countless cofounders - many of whom are related or had a close relationship before working together.

As they find out, it's difficult to keep the relationship separate from the business, so cofounders often meld their work and social lives together.

But that harmony comes with its own challenges. Like how do married couples keep business talk out of their date nights? What happens to the business when best friends have a disagreement? And can siblings put their differences aside for the sake of collaboration?

Five cofounders told us how they balance business and close relationships, from two best friends making vegan ice cream to a husband and wife starting a winery franchise.

Here are the lessons they've learned about relationships and cofounding.