All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Dear brother, we ask Almighty Allah to bless you and your brother, and to grant a good reward for your mother. Really, she made every effort to bring you up on Islamic teachings, and she was very patient with you and preferred your advantage to her own desires, as she sacrificed herself and did not marry as the common women do, only to bring you up. The best glad tiding are for her. Abu Daawood reported in his Sunnan: ‘Awf Ibn Maalik Al-Ashja’ narrated that the Prophet said: “I and a woman whose cheeks have become black, shall on the day of resurrection be like these two (pointing to the middle and forefinger); i.e. a woman of rank and beauty who has been bereft of her husband, and devotes herself to her fatherless children till they go their separate ways or die.”
Moreover, Al-Bukhaari reported in his Saheeh that the Prophet said: “I and the sponsor of an orphan shall on the day of resurrection be like these two (pointing to the middle and forefinger)”.
My dear brother! You and your mother should know that taking interest on deposited money in banks is pure Riba (interest and/or usury). Allah Says (what means): {O you who have believed, fear Allah and give up what remains [due to you] of interest, if you should be believers.} [Quran 2:278]
Besides, depositing money in usurious banks is also prohibited because it is a cooperation with them in sin. Allah Says (what means): {Help you one another in virtue, righteousness and piety but do not help one another in sin and transgression. And fear Allah. Verily, Allah is Severe in punishment.} [Quran 5:2].
Please do not deal with usury, this is a very big sin. It is a war against Allah and His Prophet as mentioned in the Quran. You are saying that you will deposit your money and take interest in order to preserve the money.
This is a mistake because dealing with usury will destroy the money and its blessing. Allah Says (what means): {Allah destroys interest and gives increase for charities. And Allah does not like every sinning disbeliever.} [Quran 2:276]
You should follow the way of piety and Allah will relieve you from all problems. Allah Says (what means): {… And whosoever fears Allah and keeps his duty to Him, He will make a way for him to get out (from every difficulty). And He will provide him from (sources) he never could imagine.} [Quran 65:2-3]
You must invest your money in lawful fields and be trustful in Almighty Allah; surely He will bless you and facilitate you all your matters. May Allah grant you a good life. As long as your grandfather determined by a will that his sons (your uncles) should give you, then it is obligatory on them to fulfill his will and they should give you a part from one third of his inheritance. If he had not made a will, they should take care of you and do good to you. But according to the Islamic law, grandsons are not eligible for inheritacne in the presence of sons.
As regards Zakaah, if his wealth has reached Nissab (Minimum amount of property liable to payment of Zakaah), and one Islamic year has passed, then you should pay 2.5% of his wealth as Zakaah.
We ask Allah to bless you and us.
Allah knows best.