(28) To establish a program to finance the construction or rehabilitation of housing designed for condominium or cooperative ownership, to convert existing housing however financed to such forms of ownership, and to finance the ownership of individual shares of or memberships in cooperative housing, and individual units of condominium housing, which mortgages for such cooperative and condominium housing are financed by the authority, and in connection therewith to make or insure first or second mortgage loans to finance the organization and the construction or rehabilitation of or conversion to cooperative or condominium housing, to assist and advise tenants during a period of conversion to cooperative or condominium ownership, and to make or insure loans to finance the ownership of individual shares of or memberships in existing as well as new or rehabilitated cooperative housing, such loans to be secured by pledges of the individual shares of or memberships in the cooperative housing purchased or by such other security as the authority shall prescribe, pursuant to such rules and regulations as the authority may determine, provided, in the case of mortgage loans or mortgage loan insurance for occupied existing housing to be converted into cooperative or condominium ownership, the authority shall determine, prior to any mortgage loan or mortgage loan insurance commitment, pursuant to rules and regulations promulgated by it, that a sufficient number of the families and persons who are tenants before such conversion have agreed to purchase individual shares of or memberships in any cooperative housing created or units in any condominium declared after conversion to ensure the economic feasibility of the conversion and to ensure that the conversion will not create undue