What is the ruling of the Sharia on not executing the will of the deceased on the grounds that "there is no will after death"?

The heirs must carry out their mother's will to wash her in her eldest son's house and to give out a portion of her wealth not exceeding one-third, as long as she willed it before her death. As for a will that comes after death, such as a dream, it is not obligatory to carry it out. You should explain this difference to your siblings so they may execute the obligatory will, for this is a part of showing devotion to their mother.