Is it considered against Islamic law for a father to sell a building to his children without charge after they agree to his marriage?

Your father's share in the house left by his wife is either a lawful gift if it was taken possession of during her lifetime, or a real sale, the price of which remains a debt on you to be distributed among her heirs after her death. However, if the sale was fictitious, intended to deprive some heirs, then it is a forbidden deception, and it does not permit you to monopolize his share to the exclusion of the other heirs.