What is the jurisprudential ruling on a father's will to his children to allocate a plot of land for his grandchildren to build a house on, knowing that they did not build on it, then one of their cousins built on part of it with their consent, and then the father passed away, followed by the builder? After that, the grandchildren demanded possession of the entire plot and the building on it, demanding compensation from their cousins or that they leave the building to them?

If the father designated a plot of land for his grandchildren and this was done, then the land is their property. If the grandchildren granted a portion of this land to their uncle by way of ownership, and he took possession of it and began construction on it, then the granted portion becomes his exclusive property and transfers to his heirs after his death. The grandchildren have no right to claim it back or demand compensation for it. However, if the grant was on the basis of a loan (for use, without transfer of ownership), then one may refer to Fatwa no. 69300. It is advisable to refer such cases to the Shariah courts.