As to all of said lands within the limits of said grant which are not owned in severalty by individuals, companies or corporations and which are in and by said decree of said court of private land claims decreed to belong to said city and cotrustee, in trust, for the benefit of the inhabitants of said grant, said city council and trustees shall have the power and authority to sell and dispose of said lands at public or private sale for the best possible price they can obtain for the same, which said sales of said lands shall be duly advertised before said sales are made. Such city council and trustee shall have the right to sell and dispose of said lands or lease or rent the same or any part thereof in such parcels and in such portions and in such manner and upon such terms as the city council of such city may deem best, and shall have the right to sell and dispose of the same for cash or on credit and may provide for perpetual ground rent in the way of interest for any unpaid purchase money and may make titles forfeitable for nonpayment of such ground rents in such manner and upon such terms as it may think most conducive to the benefit and advantage of the inhabitants of said grant, and shall make and execute and deliver all necessary deeds in the premises: provided, that the said land and no portion thereof shall be sold as above provided until said lands so offered for sale shall first be appraised by three disinterested property owners resident on said grant, appointed by said city council, at its full cash value: and provided, that no sale shall be made unless the said land so sold shall bring at such sale at least two-thirds of such appraised value.