You might want to read Numbers again. There is nothing which attests to your claim that inheritance defaults to the mother's side.Throughout the Bible, it is normally the biological father's side of the family that
determines a child's tribal identity, but in Jesus' case there was no biological father.
So tribal determination defaulted to his biological mother's side.
Mary's situation was unusual but not unbiblical. Inheritance via women became an
expedient back in Num 27:1-8.