Is it permissible to dedicate a group of Qurans on which is written: "Waqf for the sake of Allah Almighty and not permissible to sell," knowing that the buyer was unaware of this, and is there any liability upon the buyer?

May you and your mother be rewarded, and may your grandfather be recompensed for his intention. However, the endowment (waqf) was not complete because endowed Qur'ans are not permissible to buy or sell. You must return the Qur'ans to the entity for which they were endowed, if you know it, and reclaim your money from the one who sold them to you. There is no sin upon you for buying them, as long as you did not intentionally buy an endowed item.