No, you can't fight this. If a will leaves you, say, a house--for example, it says, "I leave my grandson my house"--the way it must be read is as if it said, "IF I still own my house when I pass away, I leave it to my grandson." That is, the will controls what happens to assets owned at time of death but in no way restricts what happens to them pre-death: a person may freely sell, spend, exchange, transfer, trade, gift or give away, etc. anything they own during their life and the will does not prevent that. The will only comes into effect after death, and has no affect on what is done pre-death. Thereore, your grandmother could make her son owner of her home.