My brother and my sister died before my father. Could their children inherit from my father?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

Your sister's children do not inherit from your father because they are relatives but not heirs. But your brother's children inherit from your father provided that the deceased has no male children. However, if the deceased has male children, then the grand-children do not inherit from their grandfather as they are prevented by direct heirs (the children). The Prophet said: "Give the prescribed share of inheritance to those who are liable for it and the remaining is for the nearest male relative."

Allaah Knows best.