What is the ruling on a mother waiving her inheritance from her deceased husband and her deceased son through an informal contract, knowing that the son did not distribute anything from his estate?

The share of an heir in an inheritance is a right for his heirs after his death, like the rest of his possessions. It is not invalidated by a delay in division or by the passage of time, and it does not require a waiver. Therefore, what your uncle did changes nothing, and he is not entitled to this sixth or eighth share without the rest of the heirs if the writing was a bequest to an heir, or a gift that was not taken possession of during the lifetime of the giver before her death illness, or if there was no justice between the children. It is preferable to expedite the division of the inheritance after the necessary procedures so that each heir receives his share.