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.
If the heirs are only those mentioned in the question, and the deceased did not leave any other heir, then it is only his son and his daughter who will inherit from him by Ta’seeb (by virtue of having a paternal relation with the deceased and not having an allotted share, so they get what is left after the allotted shares have been distributed). Therefore, the inheritance should be divided into 3 shares, the son gets 2 shares and the daughter gets 1 share as Allaah says (what means): {Allaah instructs you concerning your children [i.e. their portions of inheritance]: for the male, what is equal to the share of two females.}[Quran 4:11]
The grandson and the granddaughter, as well as the brothers and sisters and their children, do not get anything from the inheritance because they are prevented by the existence of the son of the deceased as it is the case here.
It should be noted that the matter of inheritance is a very serious and complex matter, so a mere Fatwa which is an answer issued according to the question is not enough. Rather, the matter should be taken to an Islamic court to look into the case and investigate it as it might be that there is an heir who would not be known except after investigation, and there might also be a will, debts, or other dues that are not known to the heirs. It is known that these rights come in priority over the right of the heirs in the inheritance. Therefore, the inheritance should not be divided without resorting to an Islamic court, if available, in order to fulfill the interests of both the living and the dead.
Allaah Knows best.