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There were two James's. Only two. James the Greater, brother of John, and James the Lesser, also known as James the Just. That's why they have those names, "Greater and Lesser".

I forgot about James the Greater! You may be correct about James the less being the same as James the Just. Hard to say though since James the less is used only once in the NT:

Mark 15:40
There were also women looking on afar off: among whom was Mary Magdalene, and Mary the mother of James the less and of Joses, and Salome;

and at this time, Judas and Simon are not mentioned, plus it would seem that it would be mentioned that Mary was the Lord's mother.

Do you know if there are any early church writings that would confirm that James the less is James the Just?

According to the Catholic Encyclopedia article on St. James the Less, the appellation "James the Just" comes from Hegesippus, quoted in Eusebius, History, book II. Eusebius doesn't use the appellation "James the Less"; he calls "James the Just" the "brother of the Lord" and "bishop of Jerusalem".

He only mentions two men named James (the other is James the Greater, son of Zebedee). Eusebius (but not Hegesippus) identifies James the Just as a "son of Joseph," I believe erroneously. James the son of Alphaeus just falls off Eusebius' radar screen. (Eusebius does not claim that James was the son of blessed Mary, only the son of Joseph.)