If the sons of Yusuf are not Muslim then they shall get no share in the property of their father. However the step brothers and sisters who are from the side of mother they all three shall get their shares from one third property. And the bhatija (son of step brother from his father) shall get the remaining two third while all the four bhatijis shall be deprived as they are among the zavi al-arham (a kind of relatives). So, all the property shall be divided into 9 shares out of which 1-1 share shall go to step brother and sister and six shares shall go to the step bhatija.
Step brother and sister 3×1= 3 shares
Step nephew 1×6= 6 shares
Total 9 shares
Allah (Subhana Wa Ta’ala) knows Best
Darul Uloom Deoband