If a couple died together in an accident, who inherits from whom?
Question

                I have a relative who died along with her husband in an accident when they had only been married for about five months. This was her first marriage but he had another wife and sons and daughters, and when he died (the first wife) was still married to him. 

My question is: who inherits from my relative who was the second wife? And what is to be included in her estate? Who is entitled to the gold that her deceased husband gave to her at her wedding? Does it go to her heirs or the heirs of the husband, or to both? How should it be divided? Please note that he has sons and daughters, and a father and siblings, and she has a mother, two sisters and a brother. 

With regard to the delayed portion of the mahr that was agreed upon in the marriage contract, should the husband’s family give it to her heirs or is her and their right to it waived? 

She had a separate house that the husband rented to be a marital home, and he furnished it and equipped it; to whom should the furniture and equipment go?

He also owned a house in which he and his first wife and children lived; can my relative inherit any part of it and of what her husband left behind, or not?.
Praise be to Allah.
    Firstly: 

    When a person dies he may be inherited from by his living 
    heirs, so it is essential to establish whether the heir was still alive 
    after the person died. In the case asked about here, if it becomes clear to 
    us that one of the spouses died after the other, even by a short moment, 
    then the one who died later inherits from the first one, then the 
    inheritance passes to his or her heirs after that. 

    But if we do not know which of the two spouses died first, 
    then the majority of scholars are of the view that it cannot be proven that 
    they inherit from one another, so neither of them inherits from the other, 
    because one of the conditions of inheritance is that we should establish 
    that the heir was still alive after the death of the deceased, and this 
    condition is not met in this case. 

    So the husband’s estate should be divided among his heirs, 
    and his wife does not inherit anything from him. 

    And the wife’s estate should be divided among her heirs, and 
    her husband does not inherit anything from her. 

    Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said, 
    concerning the ruling on a situation where a group of people who would 
    inherit from one another died in an accident. He said: When that happens, 
    one of the following five scenarios apply: 

    1.We know exactly who died last, 
    so he inherits from those who died first, and not the other way round.

    2.We know that they all died at 
    the same time, so there is no inheritance among them, because one of the 
    conditions of inheritance is that the heir should still be alive after the 
    death of the deceased, de facto or de jure, but that is not the case here.

    3.We do not know how they died; 
    was it one after another or all at the same time?

    4.We know that they died one 
    after another, but we do not know exactly who died after whom.

    5.We know who died after whom but 
    then we forgot.

    In the last three cases, they do not inherit from one another 
    according to the three imams [Abu Haneefah, Maalik and ash-Shaafa‘i]; this 
    is also the view favoured by al-Muwaffaq Ibn Qudaamah, al-Majd, Shaykh Taqiy 
    ad-Deen Ibn Taymiyah and our shaykhs ‘Abd ar-Rahmaan as-Sa‘di and ‘Abd 
    al-‘Azeez ibn Baaz. This is the correct opinion, because one of the 
    conditions of inheritance is that the heir should still be alive after the 
    death of the deceased, de facto or de jure, but this condition is not met 
    when it is not known. However the Shaafa‘is said that in the last scenario 
    these decisions should be delayed until they remember or agree, because 
    remembering is not something impossible.   

    End quote from Tasheel al-Faraa’id, p. 142, 143 

    Based on that, when dividing the wife’s estate: 

    If the husband died after the wife, then he inherits from 
    her, and her estate is to be divided as follows:

    The husband gets one half, the mother gets one sixth, and the 
    remainder goes to the brother and two sisters, with the male getting the 
    share of two females. 

    If we do not know whether the husband died after she did, 
    then her estate is to be divided among the mother and siblings as follows:

    The mother gets one sixth, and the remainder goes to the 
    brother and two sisters, with the male getting the share of two females. 

    With regard to this division of the husband’s estate: 

    If the wife died after he did, then she inherits from him and 
    his estate is to be divided as follows:

    The two wives together get one eighth, the father gets one 
    sixth, and the children get the rest, with each male getting the share of 
    two females. The siblings do not get anything. 

    If we do not know whether the wife died after him, then she 
    does not inherit from him and his estate is to be divided as mentioned 
    above. So the father gets one sixth, the first wife gets one eighth to 
    herself, and the children get the rest, with each male getting the share of 
    two females. 

    Secondly: 

    Your relative’s estate is everything that she left behind of 
    wealth that she owned. That includes her mahr that was given to her, whether 
    it was gold or cash, as well as gifts that were given to her, because they 
    became her property. 

    With regard to the delayed portion of her mahr, this is a 
    debt owed by the husband, so it must be taken from his estate and added to 
    hers, then divided among her heirs. 

    Also included in her estate is the diyah if the accident was 
    caused by an individual, whether it was her husband or anyone else and her 
    heirs asked for the diyah or it was paid by the insurance. 

    With regard to the furniture and equipment in the house, they 
    belong to the husband unless that was part of her mahr, as is customary in 
    some countries, or any part of it was given as a gift by the husband to his 
    wife. 

    Thirdly: 

    The husband’s estate is whatever he left behind of wealth 
    that belonged to him. That includes the house that he owned. This estate is 
    to be divided among all his heirs. 

    With regard to this issue of inheritance, reference should be 
    made to the sharee‘ah court so as to find out and list all those who are 
    entitled to inheritance and the estate, and to find out the circumstances of 
    death and which of the spouses died first. Because there is a difference of 
    scholarly opinion concerning inheritance between the spouses in such cases, 
    the one who should handle any cases of disagreement among the heirs is the 
    qaadi (judge). 

    And Allah knows best.