Is it legitimate and valid for a father to relinquish all his property to his son during his lifetime, without the consent of the remaining heirs, and does this relinquishment include what the father inherits after the relinquishment?

The father's relinquishment of his gift to you does not include what accrues after the contract, but is limited to what existed at the time of the gift.

If the father earned money after the contract, it does not fall under the gift and is divided as an inheritance among all his heirs.

You must also share with your brothers and sisters what your father gifted you, in order to remove injustice, unless there is a legitimate شرعي justification for that تخصيص allocation.