Holiness of Mary and Joseph Often in stain glass and other art, both Mary and Joseph are seen to have the 'halo' around them that also surround those of saints.

I was once told (by I think my religion teacher) that for Jesus, the son of God, to be born, he had to be born of parents possessing the holiness of God. Other than Jesus having to be of the house of David, were they any other requirements (preferably with a reference)? Or is this a distortion?

Also, if this was true, that only those with the holiness of God could parent His son, would that not require that all their parents before them have the same requirements to birth them?

Also, another thing I find interesting is I believe (as do my parents) is that we all possess the holiness of God, as we are all God's children with no favorites. While our decisions in this life effect our outcome in the after life, if not this one, does it in any way effect how God effects our lives other than our lack of letting him?

Sorry if I went off topic a bit with some additional questions, but if any of these are possible duplicate would love the link.
The Catholic Church has a uniquely developed perspective on this question. It is a dogma of the Catholic faith that Mary was immaculately conceived -- or in the words of Pope Pius IX:


  We declare, pronounce, and define that the doctrine which holds that
  the most Blessed Virgin Mary, in the first instance of her conception,
  by a singular grace and privilege granted by Almighty God, in view of
  the merits of Jesus Christ, the Savior of the human race, was
  preserved free from all stain of original sin, is a doctrine revealed
  by God and therefore to be believed firmly and constantly by all the
  faithful


The Pope lays out the arguments from Scripture and Tradition in the 1854 document from which that quote is drawn, Ineffabilis Deus. But to briefly address your questions from a Catholic perspective:


Yes, Mary is uniquely holy among mere human beings -- and I use the word "mere" to distinguish her from Jesus, who is human but also divine and so uniquely holy among human beings in a different way.
By the same token Mary is uniquely favored. See especially Luke 1:28, 1:30, 1:42 and 1:48, which all seem to indicate fairly clearly (whatever one thinks about the dogma of the Immaculate Conception) that Mary holds a special place in God's providence and is worthy of our special attention.1
No, there is not an infinite regress of ancestors of Mary who would themselves have needed to be just as holy -- she was personally and individually given a unique grace.
St. Joseph, being the spouse of Mary and the adoptive father of Jesus, is held in greet esteem in the Catholic Church -- Scripture attests his righteousness unequivocally, and after Mary he would have known the Lord more intimately than anyone else, at least in an earthly sense.
But Joseph is not on the same level as Mary, who is called in a true sense the mother of God. As the Wikipedia article nicely explains it, summarizing what the Council of Ephesus taught in the year 431 (principally to combat the error of Nestorius about the person of Jesus): "her son Jesus is one person who is both God and man".




1 For less clear but still evocative indications of Mary's special role, see Luke 2:35, John 2:5, and Acts 1:14. And then there are texts that have additional significance if one already accepts the Catholic perspective, such as John 19:26-27 and Revelation 12:1-6.