Ben's and Jerry's Ice Cream [duplicate]

Look at this website.

According to the website, Ben's and Jerry's ice creams would be used if Ben and Jerry had two different ice cream companies. Ben and Jerry's ice cream is used if they jointly own a company.

Actual usage by native English speakers doesn't always strictly follow this rule, but Ben and Jerry's ice cream is the most grammatically correct way to name the company.

The actual quote from the website says:

When you are showing possession with compounded nouns, the apostrophe's placement depends on whether the nouns are acting separately or together.

Miguel's and Cecilia's new cars are in the parking lot.
This means that each of them has at least one new car and that their ownership is a separate matter.

Miguel and Cecilia's new cars are in the parking lot.
This construction tells us that Miguel and Cecilia share ownership of these cars. The possessive (indicated by 's) belongs to the entire phrase, not just to Cecilia.