All perfect praise be to Allah the Lord of the Worlds. May His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
The general rule concerning inheritance is to calculate the shares according to the rules stipulated in Sharia and its isn`t permissible to change the division prescribed by Almighty Allah nor ignore it. The evidence on this is that Allah the Exalted says {What means}: "Those are limits set by God: those who obey God and His Apostle will be admitted to Gardens with rivers flowing beneath, to abide therein (for ever) and that will be the supreme achievement. But those who disobey God and His Apostle and transgress His limits will be admitted to a Fire, to abide therein: And they shall have a humiliating punishment." {An-Nisa`, 13-14}.
The wealth of the deceased is the property of all his/her heirs and it isn`t permissible to deprive some of them from their lawful shares. Even if the laws of the country where the person died are contrary to the rules of Sharia as regards the division of the inheritance whereby some heirs get a share while some don`t or they go against the division prescribed in Sharia, the heirs must re-divide the estate according to the rules of Sharia. This division can be easily figured out through issuing a deed of inheritance from an Islamic court.
In conclusion, the estate of the deceased mentioned in the above question must be re-divided according to Sharia and it isn`t permissible to deprive the parents of the deceased from their shares of their son`s estate. And Allah the Almighty knows best.