He died and left behind wealth on which he did not pay zakaah, and interest
Question

                There is a young man who has not yet reached the age of twenty, and he has two older sisters. His father died and left them an inheritance, but his father only prayed occasionally and he did not pay zakaah of 2.5% on his accumulated wealth each year. He used to spend on his household from the interest he got from the bank. My question is:

1- What is the ruling on the zakaah on this wealth that was not paid for several years?

2- How can expiation be offered for that haraam interest that he used to spend on his household for several years?

3- This man left behind a large amount of his wealth in the form of certificates that pay interest. How can these haraam certificates be gotten rid of, knowing that this young man has no experience in administering wealth or trading, and he does not even have time for that because of his studies?.

4- What are the forms of ongoing charity (sadaqah jaariyyah) that are accepted nowadays?

5- The father died of liver cancer and there were no signs of a bad end just before he died. He used to repeat the phrase Al-hamdu Lillaah (praise be to Allaah) often before he died. Is he a shaheed because he died of an internal disease?.
Praise be to Allah.
    If the deceased had repented to Allaah for not praying and 
    was keen to perform prayers before he died, then there is the hope that he 
    is a shaheed (martyr), because the Prophet  (peace and blessings of 
    Allaah be upon him) said: “The martyrs are five: the one who dies of the 
    plague, the one who dies of an internal disease, the one who dies by 
    drowning, the one who is crushed by a falling wall and the one who is 
    martyred for the sake of Allaah.” Narrated by al-Bukhaari, 2829; Muslim, 
    1914. 
Al-Nawawi (may Allaah 
    have mercy on him) said: The one who dies of an internal disease refers to 
    stomach disease, i.e., diarrhoea. Al-Qaadi said: And it was said that it 
    refers to the one who is afflicted with dropsy and his stomach swells; and 
    it was said it is the one who suffers from a complaint in his stomach; and 
    it was said that it is the one who dies from any kind of internal disease. 

    From Sharh Muslim.  

    1 – It is obligatory to pay the zakaah that is owed from past 
    years, by estimating how much he owned – each year – of permissible wealth 
    on which zakaah is due, such as currency and gold, that reached the 
    threshold at which zakaah becomes due and that had been in his possession 
    for a full hijri year, and without including the haraam interest. One 
    quarter of one tenth should be paid on that, i.e. 2.5%. Then what is left 
    for the following year should be estimated and 2.5% paid likewise, and so 
    on. 

    2 – With regard to what his heirs have consumed of interest 
    (riba), they should repent from that, if they knew that it was haraam, and 
    they should try hard to make du’aa’ for their father that he be forgiven by 
    Allaah, because consuming riba is a major sin. May Allaah protect us and all 
    the Muslims from that. 

    3 – The heirs are not entitled to anything from the 
    certificate mentioned but the original capital. It is not permissible to 
    take the haraam interest. If the bank insists that the heirs take it, it 
    should be taken from the bank and given to the poor and needy, or spent in 
    the interests of the Muslims, so as to get rid of it. See question no.
    20695. 

    If there is an Islamic bank whose transactions are governed 
    by sharee’ah, it is permissible to invest the money through them. 

    Ongoing charity (sadaqah jaariyah) may be done in many ways, 
    such as building a mosque or contributing to the building, buying books for 
    seekers of Islamic knowledge, buying Mushafs to be placed in the mosque, or 
    donating a house or shop as a waqf and stipulating that its income be spent 
    on the poor, orphans, relatives, students or others, as stated by the 
    founder, or donating money for building a charitable hospital, and so on. In 
    some countries there are organizations that are responsible for waqfs, which 
    you can contact and establish a waqf or contribute to one through them. 

    The best way in which you can benefit the deceased after his 
    death is to make du’aa’ for him and strive hard in making du’aa’ for him 
    that Allaah bestow His vast mercy upon him and forgive him his sins. 

    We ask Allaah to accept (your good deeds) and to help you to honour your father. 

    And Allaah knows best.