The "Twelve"
Jesus selected a special group of 12 men from among his followers. The lists of names of these men appear in Matthew, Mark, Luke and Acts (not John).
They are:
1. Simon Peter
2. James son of Zebedee
3. John son of Zebedee
4. Andrew brother of Peter
5. Philip
6. Bartholomew
7. Matthew
8. Thomas
9. James son of Alphaeus
10-a. Thaddeus (in Mark and Matthew)
10-b. Lebbaeus (in some manuscripts of Matthew)
10-c. Judas (Jude) son of James (in Luke and
Acts)
11. Simon the Zealot
12-a. Judas Iscariot (all but Acts)
12-b. Matthias elected to replace Judas Iscariot (Acts only)
Notice that 4,5 or 6 of the Twelve are related (1 and 4, 2 and 3, and possibly 10-c with 9 or 2).
Were any of Jesus' Brothers among the Twelve?
Some Traditions try to equate 9 James and 10-c Judas with two of Jesus' four brothers (James, Joses/Joseph, Simon and Judas) mentioned in Mark 6:3 and Matthew 13:55. However, this is discounted by modern scholars since Jesus' brothers are referred to as a distinct group (Acts 1:13-14, I Cor 15:5-7) and were not believers during his ministry (John 7:5 and possibly Mark 3:21,31). Jesus' brother James is called an "Apostle" (Gal 1:19) and is especially important in, if not the head of the early church in Jerusalem. He is the traditional author of the Epistle of James. Jesus' brother Judas is the traditional author of the Epistle of Jude.
Were the Twelve "Apostles"?
Interestingly, Jesus only refers to the Twelve as "Apostles" once (Luke 11:49). Many scholars believe that "Apostle" is a post resurrectional title used somewhat broadly in the early church and only retroactively applied to the Twelve. It is used only once in Mark (6:30) and Matthew (10:2), and six times in Luke (6:13, 9:10, 17:5, 22:14, 24:10 and 11:49).
Also, there are other people referred to as Apostles in the New Testament who are definitely not part of the Twelve. These are:
Paul (I Cor 1:1)
James the brother of the Lord (Gal 1:19)
Barnabas (Acts 14:4, I Cor 9:6 with 4:9, Gal 2:9)
Andronicus (Rom 16:7)
Junias (Rom 16:7) a women's name!
And possibly Sylvanus, Timothy and Apollos by indirect reference.
In summary all 3 groups are heard from when Paul tells us that the resurrected Jesus "was seen by Cephas [Simon Peter], then by the Twelve. After that he was seen by five hundred brothers ... Next he was seen by James [Jesus' brother]; then by all the apostles. Last of all he was seen by me..." (I Cor 15:5-8).
Counting Jesus' brothers there could be as many as 26 "Apostles" in the New Testament