بسم الله الرحمن الرحيم
(Fatwa: 1056/921/SN=8/1438)
If your grandfather, grandmother died before the death of your father then in the question mentioned above all the property of your deceased father shall be divided into 8 shares, after paying due rights proceeding inheritance. Out of the total, your mother shall get 1 share, each brother shall get 2-2 shares while 1-1 share shall go to each sister. The detail of Shariah division is as follows:
Wife: 1 x 1 = 1
Sons: 2 x 2 = 4
Daughters: 3 x 1 = 3
Total 8 shares
Allah knows Best!
Darul Ifta,
Darul Uloom Deoband