[annalex]

....the context of Matt. 12:46-50 and Luke 8:19-21 shows how the word “brother” is being used, as sharing a parent

How does the context "show" that?

[count-your-change]

Someone says to Jesus, “Your mother, YOUR brothers..”. They were brothers specific to him and Jesus makes a comparison of his mother, brothers and sisters by birth with those counted as such by doing God’s will.

It is not “mother and anepsios (cousin) and sisters”.