What is the ruling of Islamic law regarding a husband who drinks alcohol daily and claims it is not forbidden, and accuses his wife of corruption with her nephew?

Drinking alcohol is forbidden and considered a major sin. Its prohibition is established by the Quran, the Sunnah, and the consensus of Muslims. Anyone who deems it permissible is considered a disbeliever. The wife must try to convince her husband to abandon it, and if he is not convinced, she has the right to seek a divorce.

As for a husband accusing his wife of corruption without proof, this is a grave matter in the sight of Allah. If the accusation reaches the level of adultery with her nephew, then this is an accusation against chaste women, which is one of the major sins that necessitates the punishment of qadhf (false accusation of unchastity) upon the accuser.