I skimmed through this and I am somewhat familiar with the debate generally.  

I am not sure what in any of the texts implies that the brothers and sisters (even assuming they meant brothers and sisters as we understand the term) would have been the sons and daughters of Mary.  

I do agree that if they were calling Jesus Crazy then they likely did not mean brother in the sense of following Jesus – but see below where it is possible they were indeed on the very inside.  

The passage where mark talks about his family calling him crazy is pretty vague.

“Then Jesus entered a house, and again a crowd gathered, so that he and his disciples were not even able to eat.  When his family heard about this, they went to take charge of him, for they said, ‘He is out of his mind.'”

Mark 3

When they heard about what exactly?  I mean I assume it is when they heard he was driving out demons.   Or is it when they heard a crowd gathered?  

One of the interesting things about Mark is Jesus is very secretive.  Some have suggested that Jesus equates people acknowledging him as messiah with his death on the cross.  So it seems Jesus does not want people to know he is the messiah because he knows that will bring his death.  Did his close family believe this as well?  Is that why they tried to brush this off and say he was crazy?  I am not sure that is entirely consistent with the text.  But if people are telling the family he is doing these wondrous deeds why would that lead the family to say Jesus is crazy.  Wouldn’t you think the family would just say those making the claims are crazy?  It seems at least possible the family wants to “take charge of him” in order to make him stop revealing he is the messiah and that is why they are trying to claim he is crazy.    

Here is a podcast (the one called “no sign for you”) that talks a bit about markan secrecy:

** you do not have permission to see this link **

Yes it is speculation but the reasons for Markan secrecy are unclear to say the least.