Firstly, please understand that we as Muslims, cannot declare any Ex-Muslim, who previously believed in Islam & now has left it becoming a Non-Muslim, as an “Apostate/Kafir/Murtad”. This is not our authority or responsibility. Our responsibility is to guide our brothers, pray for them & not Judge them. If they don’t return than its their choice. We should fulfill our responsibility & leave the matter in the hands of Allah. Nowhere in the Quran or Hadith is this authority to declare Ex-Muslims as Apostates, given to any Muslims. Only Allah has that authority and Allah only uses this authority through his Prophets. Besides the Prophets none else can claim to have a special authority from Allah and assume the responsibilities of Prophets. I am sorry but Passing on Fatwas like this and declaring anyone as Kafir or an Ex-Muslim as Apostate/Murtad is an extremely sectarian mindset that has destroyed our unity from within giving rise to heinous crimes and even civil wars. Therefore we should be extremely careful while choosing our words.
The Four Sunni Fuqaha/Jurists such as Imam Abu Hanifa, Malik, Shafaee & ibn e Hambal were great Muslim Scholars and they served as great interpreters of the legal tradition/Shariat in Quran and Sunnat during their times. However they were still Human beings capable of errors. With due respect to them, they made an error of Judgement concerning this ruling. And they considered a Specific ruling allocated specifically by the Prophet Muhammad(saw) for a particular group & individuals and they applied it generally for all Muslims. However its clear, in the light of Quran, that the Hadith of Apostasy are dealing with Specific audience of the Prophet during his time only. Meaning the punishment of death for the Mushriqeen & Ahl e Kitab of Arabia during the 7th Century who initially became Muslims but later on reverted back to their previous faiths or left Islam altogether. These legal rulings concerning Apostasy or Irtidaad are not to be followed by the Muslims today as Hukam of Shariat. They are not applicable today after the death of Prophet.
Now coming to the Specific example you mentioned here. I personally do not know much about this couple’s situation, hence i cannot comment much & My apologies in this regard. But what little i know from your message i will try to explain inshAllah to the best of my knowledge. The Quran is silent on the specific issue of a Spouse leaving Islam & becoming Non-Muslim. This is a matter that must be sorted out between the Spouses themselves. If the spouse who is a strong Muslim feels that Islam is an essential part of his/her family and must to be kept to raise their children than he/she should think about separating temporarily from the Non-Muslim Spouse until the children become adults & able to consciously choose religion for themselves. Until a time that they become adults, the small children in the house should not influenced by this conflict and must be single minded in following the religion of their Muslim Parent.(i.e. Islam). After they become adults the couple can come together again and decide. By this time the Children should be given freedom to choose whatever religion they want to adopt, whether remaining a strong Muslim or leaving Islam, its upto them and Parents should not interfere or impose their choice on their children. Now they can only teach and guide them.
Secondly the Quran does give some guidance concerning Mushriq Spouse. Its prohibits to marry a Mushriq Man or a Woman. And similarly the Marriage/Nikkah is considered terminated if a Muslim Spouse converts to Mushriq Religion. We have numerous examples from the Prophet’s and Companions lives where the Spouses left their previous husbands or wives, after becoming Muslims & remarried among Muslims from the Muslim Community. Other than that I do not see a specific ruling in the Quran.
The Marriage is valid and legal in the light of Quran and Sunnat. The couple should sort this out among themselves. There is no need for any dissolution of Marriage contract. The Strong Muslim Spouse should continue to be a good example of pious Muslim to convince her/his Non-Muslim Spouse to revert back to the Faith. But should not force. InshAllah hopefully seeing the beautiful example of acceptance and tolerance within the Family the non-Muslim Spouse may consider turning back towards Islam. One should be optimistic rather than Pessimistic. Best of Luck to the Couple and May Allah make this issue easy for them. Ameen 🙂