I think Ol' Mom was content to honor the decision of her Lord. As for His siblings, what could they say? They, along with the rest of them, fled at the crisis hour. Only John was there, and it was he whom Christ loved. It actually makes perfect logical sense. I am granting that Mary and John both knew who Jesus was, but not so with Christ's siblings, necessarily. I would have made the same decision, regardless of custom. It was reasonable, and Mary obviously didn't object.
Now, regarding what Jesus "thought of His family", I look to the following:
Mark 3:31-35 : 31 Then Jesus' mother and brothers arrived. Standing outside, they sent someone in to call him. 32 A crowd was sitting around him, and they told him, "Your mother and brothers are outside looking for you." 33 "Who are my mother and my brothers?" he asked. 34 Then he looked at those seated in a circle around him and said, "Here are my mother and my brothers! 35 Whoever does God's will is my brother and sister and mother."
This shows what JESUS thought. This CATEGORICALLY tells me that Jesus did not feel beholden to custom as to who should care for His mother. Jesus chose His brother John, who was the only brother with Him at the end.
Obviously, Jesus loved John. That is a tautology. Do you think He didn't love the other Apostles as much?
To me it is strange modern evangelicals desire to throw-in with Helvidius, and even repudiate the reformers as a way of doing that. However, free will being what it is, and antipathy and opposition to the Catholic Church acknowledged, I am not surpised at anything anymore