This has been a difficult question for me to formulate because there are so many tangential thoughts which led to it and stem from it. I have tried to weed out as many bunny trails as I could so, please forgive the somewhat scattered nature. Hopefully the surrounding information can help clarify the intent of the main question which I have emboldened.
Luke 2:4 gives what appears to be two reasons that Joseph went to Bethlehem (the city of David) with his family in response to the census decree of Caesar Augustus: One, that it was his Joseph's own city, and two, that Joseph was of the house and lineage of David:
And it came to pass in those days, that there went out a decree from Caesar Augustus, that all the world should be taxed. (And this taxing was first made when Cyrenius was governor of Syria.) And all went to be taxed, every one into his own city. And Joseph also went up from Galilee, out of the city of Nazareth, into Judaea, unto the city of David, which is called Bethlehem; (because he was of the house and lineage of David:) To be taxed with Mary his espoused wife, being great with child. - Luke 2:1-5
My primary question is: What is the connection between Bethlehem being Joseph's "own city" and Joseph being "of the house and lineage of David"?
This question arises from a conversation with a friend as we wondered why Joseph and Mary were unable to find lodging in "his own city". Even if he had no home of his own would he not have had close relatives or friends who could have taken them in?
If Bethlehem was not his actual home or birthplace but was "his own city" only because he was in David's lineage then, why David's lineage? Matthew's gospel lists Joseph near the end of 28 generations. Why, for example, did Joseph not have to go to the city or area of Paddan Aram where Judah was born or the cities of any of the others listed in his genealogy, including even his own father Jacob/Heli?