Is shunning a brother who lives in sin, having abandoned his wife and daughter for six years, considered severing ties of kinship, and does it entail sin?

If your brother engaged in illicit relations and was absent from his family without a valid excuse, he committed an evil act and wronged them.

His marriage is permissible, provided the wife is a chaste woman of the Book and he deals justly between his wives. Documenting the marriage in courts is not a prerequisite.

Your abandonment of your brother, if for a legitimate Shar'i reason, is not considered a severance of ties. The matter revolves around the Shar'i interest.

A Muslim is advised to reside in Muslim countries.