I’m not really sure what information you are seeking… but based on the title of your thread (“Mother of Jesus”) and the content of the passage you’re interested in (concerning Jesus’ “brothers and sisters”)… I think you’re asking about the family of Jesus and the status of Mary, His Mother? Please correct me, if I have misunderstood.
I will try to tell you, what I know. Recently, on EWTN I watched a series of talks, given by Dr. Scott Hahn (former evangelical… and now convert to the Catholic faith). Dr. Hahn is Professor of Biblical Theology at Franciscan University. The series was called “Hail, Holy Queen”. They discussed the very passage that you refer to.
I learned that in the Hebrew language… AND in the era, in which Jesus lived (on earth)… the terms “brother” or “sister”… had a very wide range of understandings. The term “brother” was not understood in the same way, that WE understand it… here in the 21st Century.
In Jesus’ time… the term “brother” or “sister” was often used in reference to ANY family member (uncles, aunts, cousins… and even members of the same ‘tribe’, if you will). The term “brother” or “sister” did not necessarily denote siblings.
Therefore, this passage in no way diminishes the Catholic Doctrine of Mary, the Mother of Jesus. She was a Virgin, before… during and after His birth. And she had only ONE Son… Jesus, Our Lord.
And the second part of the question… when Jesus asked “Who are My mother and My brothers”… well, Our Lord Himself, explained what He meant… when He finished the statement… “Anyone who does the Will of God”. He is saying, that we are His “family”, if we do His Will.
Hope this helps. God bless.