What is the ruling on performing the night vigil prayer (Salat al-Layl) in congregation, and does this include a husband praying with his wife?

The Fatwa's Summary:

If the disbeliever is not hostile, there is no harm in treating them kindly.

Kind treatment is required for everyone, even non-hostile disbelievers. If the disbeliever is a dhimmi, a mu'ahid, or a musta'min, there is no harm in dealing with them in terms of buying, selling, renting, and residing, as long as it does not lead to forbidden affection and love, or confusion in religion. Kind treatment towards them does not mean alliance or love; rather, it is a form of showing kindness to them.

It has been authentically reported from Asma bint Abi Bakr (may Allah be pleased with her) that she said: "My mother came to me while she was a polytheist, during the time of the Messenger of Allah (peace and blessings be upon him). So I asked the Messenger of Allah (peace and blessings be upon him) for a fatwa, and I said: 'My mother has come to me, and she desires [my kindness], should I maintain ties with my mother?' He said: 'Yes, maintain ties with your mother.'" Agreed upon.

Many scholars have used this hadith and others as evidence for the permissibility of maintaining kinship ties with disbelieving relatives, being kind to them, and doing good to them, as long as they are not hostile to Islam and Muslims.

Therefore, if the disbeliever is not hostile to Muslims, there is no harm in treating them kindly, though it is preferable to avoid it if possible.

And Allah knows best.