Jesus is the son of God, Jesus is the son of Joseph. Which one is it? This confuses me and how can Jesus be a descendant of the kings of Isreal if he is the son of God?
Jewish identity is matrilineal. (In other words: the biological role of biological fathers does not count when it comes to the "Who is a Jew?" question.)
If the person we now understand as Jesus did actually exist back then, and if that person was indeed a Jew, then he inherited his Jewish identity through his mother...who might well have been related in some biological way to "the kings of Israel."
During that time period, that entire part of the Middle East had many religious teachers [some Jewish; some not] who traveled from place to place, teaching their take on matters religious.
I am Jewish now, but I grew up going from Christian church to Christian church as the guest of one or another of the families "on the hill" [we all lived on the same hill in Woodland Hills], most of whom went to some kind of Christian church quite regularly, and it was always my understanding from those different denominations [Congregational; Lutheran, Church of Christ, Baptist, etc., with a bit of Catholicism added to the mix] that "everyone" is [supposedly] the [offspring] of God...so if "everyone" qualifies, then it is no big, or even remarkable, situation for any given person to be the "son" or "daughter" of God.
The two things--being the "son of God," or the biological legacy of "the kings of Israel"--do not constitute an either/or situation.
Did you mean Jesus the son of David of the tribe of Judah?
Both Matthew and Luke went to great lengths to show Jesus as a royal descendant of David and hence the rightful king of Israel.
There was a branch of early Christianity that believed Jesus was a mere human and not until later was he declared the son of god. Hebrews 5:5 "Thou art my son, today I have begotten thee."
Somewhere in time Jesus went frim symbolic begotten to physical begotten.