Is the contract written by the father for the sale of the apartment to his sons before his second marriage legally valid, and therefore does the wife have no right to this apartment?

This fictitious contract is not considered a sale due to the absence of consideration. If it was intended as a gift, it is void because the gifted item was not taken possession of, and because it is in the category of a bequest to an heir. Therefore, the apartment is considered part of the deceased's estate and shall be divided among all his heirs.