For even his brothers didn't believe in him.
John 7:5
Before that they said:
...If you do these things, reveal yourself to the world."
John 7:4
So, they admitted Jesus had done impressive things, but still didn’t believe in him. I think it is interesting question why they didn’t believe. But, I don’t think Bible answers to that and I don’t think it would be good if I would make up some explanation that is not based to anything. But, the fact seems to be that many people reject Jesus, not all agree with him. I don’t think it means Jesus is not right. I think Jesus told the truth and truth just is not what many people like.
… Where then did this man get all of these things?"…
Matt 13:55-58
I think that is excellent question, if Jesus was just brother of them, why was he so different that even those who didn’t follow him, thought he had something special? And why did they not believe, if they themselves saw what Jesus did and thought it was something special? Did he invent the steam engine or describe the theory of relativity?
It is also interesting why do you think his mother didn’t believe when those scriptures don’t say so?
Newton got his knowledge by his eyes, by watching nature. Most of us can see the same things and he really has no knowledge that would be special. Same is basically with Einstein. Both of them stated basically the obvious. Many could have probably done the same long before them, but probably it was too obvious for them.
What is more important seems to be a matter of opinion, but I think what Jesus said is far more important and useful.