What is the jurisprudential ruling concerning the children's objection to their deceased father's transfer of ownership of half of his house to one of his wives twenty years before his death, and their doubts about the authenticity of the signature, especially since the contract was not registered and only recently surfaced?

The two wives who passed away before the husband do not inherit anything from him, because the condition for inheritance is the survival of the heir before the death of the inheritor. As for the contract of sale of the house to the surviving wife, it is valid if proven by evidence (witnesses or authenticated contracts), and its validity is confirmed by the Sharia courts. If this is proven, it should be acted upon; otherwise, the wife inherits her legal share (one-eighth if there are children, and one-quarter if there are none). If there are multiple wives, they share the same portion as a single wife equally. Everyone must fear Allah and not take what is not rightfully theirs.