I haven't seen the show, but I did read an article this morning about it. Bascally my understanding is that the Arameic writing on the tomb is corroded enough that the inscriptions could be misinterpreted.
Based on the names they listed of the other family members, I would have 2 questions right away: 1) One of the tombs is translated as Mary, the Master. They're theory is that this is Mary Magedeline (sp?). What would she be the master of?
2) How many other people were named Jesus, Mary, Joseph, Judah in that time? You look at the 16th century and there were a lot of Henrys, Elizabeths, Marys, etc.
Unless they build a time machine and go back 2,000 years. they'll never know.
And why haven't they found anything on Mohammed? He was a man too.