Earlier quoted context omitted.
Considering it is illegal in the UK and frowned upon by the IRS, it leads me to think you are confusing adoption of children with the adoption of adult men. Note how often these adult men are being adopted along with marrying the daughter of the family. I dare say outside of Japan such an arrangement would be considered weird.
> being adopted along with marrying the daughter of the family. How does that work? They become both husband and brother to the same person?
In practice what it means is that the couple adopts the family name of the wife, not the husband, which is the name associated with the family business that he's taking over.