Doubting whether deceased's wife was Muslim at time of marriage
4-6-2016 | IslamWeb
Question:
Assalaamu alaykum. Please calculate the inheritance according to the following information: - Does the deceased have male relatives who are entitled to inherit: (A son) Number 1 - Does the deceased have female relatives who are entitled to inherit: (A daughter) Number 1 (A wife) Number 1 - Additional information: A man dies leaving a wife and a daughter. He has a son from his previous marriage, the wife has two sons and a daughter from her previous marriage. A day before their marriage, he wrote a 'marriage contract' saying that he was transferring all his property to the wife. The 'contract' was signed by him and two witnesses, but not by the wife. There is now the question whether the wife was Muslim at the time of their marriage because there is evidence that shows that she divorced her previous husband in a civil court (her country has a sharia court that governs Muslim marriages). Her marriage certificate with the deceased says that she is Muslim, but there is no evidence to show that she converted to Islam in the time between her divorce and her marriage to the deceased. In the given circumstances, who is entitled to inherit his property, which is quite substantial? Thank you, and may Allaah reward you.
Answer:
All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ʻalayhi wa sallam, is His slave and Messenger.
Your question includes several complex issues that cannot be addressed in a mere fatwa. Rather, these issues cannot be settled except by referring them to a sharee'ah court. Nevertheless, we shall mention the religious ruling on some points in your question:
1) If the husband transferred all his property to his wife as her Mahr (bridal gift), then that is permissible and valid. There is no limit set by Islamic Law for the maximum amount of Mahr. Ibn Qudaamah 
wrote, “There is no maximum limit for the Mahr according to the consensus of scholars, as stated by Ibn ʻAbd Al-Barr, and Allaah, The Exalted, says (what means): {But if you want to replace one wife with another and you have given one of them a great amount (in gifts), do not take (back) from it anything...} [Quran 4:20]” [Al-Mughni]
If the husband intended to offer all his property to his wife as a gift (Hibah), then it is a valid gift. The sane adult Muslim can offer whatever he wishes of his wealth as a gift as long as his legal capacity is not limited in any respect. Ibn Rushd wrote, “Scholars agreed that the (legally competent) Muslim individual is entitled to offer his whole wealth as a gift to a non-heir...” [Bidaayat Al-Mujtahid]
However, this gift is not effective unless the wife has taken the wealth into her possession in terms of disposing of it in the way that the owner of wealth does before the death of the husband or what is similar to death in this regard, such as bankruptcy. Ar-Rawdh Al-Murbi' ʻala Zaad Al-Mustaqni' reads, “The gift becomes effective by possession with the permission of the gift giver. It has been reported on the authority of Maalik that Abu Bakr gifted his daughter ʻAa'ishah 
twenty wasqs (share of the crop [one wasq approximately equals 132 kgs]) of his land in Al-ʻAaliyah. When he fell ill (shortly before his death), he told her, 'O daughter! I had offered you twenty Wasaq earlier as a gift; if you have already taken the gift into your possession, then it is your rightful property; otherwise, it is part of my estate that is to be divided among the rightful heirs according to the Quran.'”
2) If the wife's conversion to Islam is established, then she should be treated as a Muslim. She is not to be declared a non-Muslim merely because she was divorced from her ex-husband in a civil court. The basic principle is that her Islam is established until her apostasy is proven with certainty. ʻAbd Ar-Raheem As-Salami wrote, “Whenever an excuse that constitutes a religious impediment to declaring a Muslim as a non-Muslim is found, he is not to be declared a non-Muslim, because the basic principle is that his Islam is established (until proven otherwise with authentic proof)...” [Sharh Risaalat Al-ʻUboodiyyah by Ibn Taymiyyah]
As for the division of the estate in this case (if there is an estate), then if the wife is considered among the rightful heirs, she is entitled to one-eighth of the estate as a fixed share because the deceased has children; Allaah, The Exalted, says (what means): {...But if you leave a child, then for them is an eighth of what you leave...} [Quran 4:12] The remainder of the estate should be divided between the son and the daughter; the male gets twice the share of the female. Hence, the estate should be divided into twenty-four shares; the wife gets one-eighth (i.e. three shares), the son gets fourteen shares, and the daughter gets seven shares.
If the wife is not entitled to inherit, then the estate should be divided into three shares; the son gets two shares and the daughter gets one share.
As we mentioned earlier, the question has some ambiguous points and overlapping rights. It cannot be decided by a mere fatwa. You should refer the case to the sharee'ah court.
Allaah knows best.