What is the ruling on disposing of a grandfather's will to his corrupt grandchildren who are drug addicts, if handing over the land to them will lead to its sale and the spending of its price on unlawful things?

Implementing the will of the deceased is obligatory with one-third of their wealth. The sin of not implementing it falls upon the one who alters it, not the deceased, unless the legatee is an heir, in which case the bequest to them is not valid, due to the Prophet's (peace be upon him) saying: "There is no bequest for an heir." Grandchildren do not inherit in the presence of direct children. Therefore, your grandfather's bequest of this plot to his son's children must be implemented if they are not heirs, even if they are corrupt and use drugs. In this case, the plot should be handed over to the Islamic judiciary to appoint an overseer for it, and they should only be given what they need, so that it is not used to disobey Allah. You must strive to rescue them from perdition and guide them towards good.