How is the relationship of loyalty and disavowal applied with a Christian wife, taking into account the difference between righteousness (birr) and affection (wudd)? And is it permissible in the night prayer to suffice with two rak'ahs while prolonging the recitation?

The disbeliever is disliked for his false religion, but he may be loved from another perspective, such as a parent's love for their child or a husband's love for his wife. Natural love does not contradict religious hatred. So, the love for مشركون (polytheist) parents is natural, but they must be hated for the sake of Allah. The same applies to loving a Kitabiyyah (People of the Book) wife. It is permissible for natural dislike to coexist with religious love, such as in jihad.

As for prayer, the Prophet, peace and blessings be upon him, prayed two rak'ahs and did not pray a single rak'ah. The matter is broad concerning night prayers, and following the manner of his prayer and his standing in prayer at night is best.