Judas is either the brother or son of James, depending on whether you are reading the KJV or the RSV. Assuming this James to be James Alphaeus, we either have three Alphaeus brothers, or two brothers...
Judas iscariot was the one who betrayed Jesus to the Pharisees for 30 pieces of silver. He took them to the place where Jesus and his disciples where, and then he gave Jesus a kiss, to show them...
Not normally, because there were two disciples of Jesus with the names Judas. The Judas that betrays Jesus is generally called Judas iscariot so you can tell them apart.