What is the plural of Ross?

'Ross' is a proper noun and it is the name of a person. As it is the name of one person, which is singular. So, as a matter of style,one would generally avoid using plurals in such cases. If there are too many persons with the same name, one can say "Different persons with the same name 'Ross'..."

That was a very bad answer. It's Rosses. "The Rosses have a dog."