What is the ruling of the Sharia concerning dealing with a son's claim that the apartment owned by his deceased father is originally his property, and that he nominally registered it in his father's name for the father to live in? And must the siblings accept his claim, or should the inheritance be distributed according to the apparent ownership?

The son should have made his agreement with his father, that the apartment was not his property, a witnessed one, or the father should have informed his children of this to safeguard his son's right. If the father did not inform the children and the son did not have witnesses, then the heirs have the choice to either believe the son and grant him the apartment, or reject his claim. In case of rejection, the son can take the matter to court, and then the judge will ask him for proof to substantiate his claim. Otherwise, the property will be distributed according to the Islamic legal division of inheritance. There is no sin upon the heirs if they do not know his truthfulness or if he has no evidence, for the Prophet, peace and blessings be upon him, said: "The burden of proof is on the claimant, and the oath is on him who denies."