What should a man do whose wife and her family reject the niqab and consider it a custom, and she demands a divorce after he insists upon it?

Covering the face is a matter of scholarly disagreement, though the preponderant opinion is that it is obligatory. A wife must obey her husband if he commands her to wear it, unless she does not believe it is obligatory due to the strength of her own evidence or because she follows a scholar she trusts. In such a case, the husband does not have the right to compel her. It is advisable to be patient with one's wife and try to convince her with kindness.