بسم الله الرحمن الرحيم
(1, 2) If both the children (16 and 10 years of age) are the sons of the deceased wife then all the property of the said wife shall be divided into 24 shares according to Shariah. Out of the total you (husband) shall get 6 shares, while each parent of the deceased wife shall get 4-4 shares, while each son shall get 5-5 shares. In this case, the brother and sister of the deceased wife shall get nothing. If the deceased has not made a will of paying fidyah of her missed fasts then it is not necessary and wajib on her heirs to pay it. Yet, if you or some other heir want to pay the fidyah of the fasts missed by the deceased then it is allowed to do so. But paying fidyah before dividing the property is only lawful in case when all the heirs are adult and all show their consent for the same, otherwise not. The fidyah of one fast is equal to Sadaqah Fitr i.e. 1.574 kg and 640 milligram wheat.
Allah knows Best!
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.