What is the ruling regarding a grandmother's will to donate 2000 dinars to the mosque if her children do not carry it out due to their difficult financial situation?

If the grandmother bequeathed two thousand dinars to the mosque from her own wealth, her will must be executed from one-third of her estate, even if the condition of her heirs is unsatisfactory. If the bequest exceeds one-third, the excess is returned to the estate unless the adult heirs approve it. It is not permissible to alter a permissible bequest due to the condition of the heirs, as Allah (the Most High) says: "Then whoever alters it after he has heard it – the sin is only upon those who alter it. Indeed, Allah is Hearing and Knowing."

However, if she instructed one of her children to give the amount from his own money, and he is unable to do so due to his straightened circumstances, there is no blame upon him, as Allah (the Most High) says: "Allah does not charge a soul except [with that within] its capacity." He should pray for her mercy, and if he is able to execute the bequest in the future, that would be an act of filial piety towards her.