In accordance to LDS doctrine, would Mary & Joseph need to be sealed (by proxy) in the temple? It is my understanding that the LDS faith places great emphasis on the family unit  because they believe that through the sealing powers performed in the Temple by the holy Melchizedek priesthood, these families can live "together forever." The sealing aspect is not only important for uniting the family for all eternity, but for reaching the highest degree of glory in the Celestial Kingdom. And for those who have passed on who hadn't had the opportunity to do their own work (which is why the Church invests so much time in doing genealogy), the LDS members can vicariously do these sacred ordinances for these individuals. 

Since we know that Mary and Joseph are undoubtedly one of the most righteous couples/parents, and are deserving of the highest degree of glory in the Celestial Kingdom, has the LDS Church performed their ordinances by proxy for them? If so, would they seal Christ to Joseph? 

Am I right in assuming that in Christ's time, sealings were not performed in the Jerusalem Temple?I suppose the same could be said for all the righteous Biblical figures? These answers may not be answerable, but I wasn't sure if the LDS Church has any statement on it or not. 

We can assume, well, "I'm sure they are taken care of... don't worry about it." But we know that Christ was an example, and while He was sinless, He still entered the waters of Baptism to show us the way. So I'm just curious if the LDS Church has mentioned the other sacred saving ordinances (according to LDS beliefs) pertaining to Christ and His family?
Mary and Joseph must be sealed by proper authority (a Melchizedek priesthood holder with the authorization to perform the sealing) in order to receive the blessings of the sealing ordinance, including inheriting the highest degree of Celestial glory.  This is true for all of God's children.  I doubt an exception would be made for them.

What we do not know is when Mary and Joseph received this ordinance, if they received it yet at all.  That is not officially part of Mormon doctrine or records as far as I know.  It is possible they were sealed by Jesus and/or the apostles while they were living or had their ordinances performed vicariously under the authority of the apostles after they passed away, but it is not certain.

In essence, they are required to be sealed, but the Church does not claim to have official records of their sealing.  Due to the current policy against performing ordinances for famous persons (as well as the uncertainty you mentioned), it is unlikely this ordinance will be performed in the near future.