In Mark 3 Jesus family shows up wanting to talk with him, and nervous about what he is doing.
His mission: to proclaim his divinity, heal people as a supportive aspect of that, and to draw people to Him had to have been hard to understand.
But, on a basic human level it was hard for his family (in the beginning) because he was different. Jesus grew up, he became more of Himself – like may of us. When the voice came from Heaven, “This is my beloved Son, in Him I am well-pleased”, everything was different – for Jesus, for his family, for the world. Often our families either don’t deal with or don’t know how to deal with our grown up selves. Sometimes this is because we are more grown up and sometimes less. Family is difficult because they have been with us for so long – therefore when we change (or, fail to change) it is disruptive. It is often the most disruptive when there was a strong desire for change… And, then it happens.
Matt Blazer's Blog 
Mark’s Gospel does not have the virgin birth story. This story of Jesus’ beginnings appears only in the Gospels of Matthew and Luke. The family of Jesus thinking he may be crazy in the Gospel of Mark makes sense when you remember that this depiction of Jesus’ life implies that he was just born like everyone else. Read each Gospel and interpret it on it’s own; do not meld them all together. Then the idea of Jesus’ family calling him crazy will make sense from the perspective of Mark’s Gospel.