Is Joe plural or do you need an s?

There are two Joes on my mother's side of the family. (Two Joe? Really?)

You're mixing two things. Game animal names get the singluar even when in groups to groups: deer, moose, sheep, bison, salmon, pike, trout, fish, and swine. But outside these hunting uses, many of these will be pluralized. You can chase a school of fish, but you sleep with the fishes.

Some Middle English -en plurals are preserved: oxen, children, brethren. A few ablaut plurals are also preserved from Middle English: feet, geese, lice, men, mice, teeth, women.

But the plural of Joe is Joes.

Since you would say "I am having an arguement", it is proper to say "My brother and I are having an arguement". Use the same form that you would alone, and put yourself at the end of the list. Please allow me to explain becomes please allow John, Jim,and me to explain.

Joe by itself is not plural. You wouldn't say "Look at those Joe!" You would say "Look at those Joes!" The word "those" is plural so "Joe" has to be plural, as with all other names.

add an s