Do the grandchildren of a son who died before their mother (grandmother) inherit from this grandmother?

What the court official informed you is correct: your brother, who passed away before his mother, does not inherit from her, due to the absence of the condition that the heir must be alive after the death of the inheritor. His children do not inherit from their grandmother because they are excluded by their paternal uncles, who are closer to the deceased. It is recommended that the heirs bestow something upon their brother's children, in accordance with the verse: "And when [other] relatives and orphans and the needy are present at the time of division, then provide them [something] from it and speak to them words of appropriate kindness" (Quran 4:8), and they are the most deserving of this gift, and their right is confirmed if they are orphans.