Is it illegal for the parent company to grant the private seal to the subsidiary company?

Illegal. It is illegal to carve the official seal privately, regardless of the water prize or not. The person in charge of the official seal enterprise holds the ID card and photocopy, and the original and photocopy of the valid industrial and commercial business license. After the public security brigade of the county (city) District Public Security Bureau where the enterprise is located handles the relevant official seal engraving procedures, it will be engraved in a place with engraving qualification.