Does the grandson of a maternal grandfather, who has no descendants other than his sister's son, inherit from him, even without a will or a direct heir?

It is not clear to us, from the questioner's inquiry, who the grandfather whose son passed away is. If the deceased is the son of the questioner's paternal grandfather (i.e., the questioner's paternal uncle), then the questioner and his male siblings are the deceased's nephews. Consequently, they are his 'Asabah (agnate heirs) and inherit what he left behind, provided there are no heirs closer to him. The sister's son does not inherit when there are 'Asabah. The matter of inheritances must be referred to the Sharia courts to verify them and ascertain any wills, debts, and other rights before distributing the estate.