Wills are not valid under Torah law; upon a person's death, all property passes to his natural heirs. One of the possible correct ways is to to stipulate that the gift takes effect “from today and after death.”
Under
this clause, the gift is granted to its beneficiary in two stages: the
property itself is granted immediately, the benefactor thereby
relinquishing his right to transfer it to anyone else. However, the
right to the property's yield (i.e. including such things as produce
and rental income) is not granted to the beneficiary until the
benefactor's death. Thus the benefactor continues to enjoy the use of
his property for the reminder of his life.