There should be a written tenancy agreement between the landlords and tenants. The tenant must be given time to read and understand the tenancy agreement before being asked to sign. Please find attached a pro forma tenancy agreement for landlords and tenants which can be accessed here.
Additional terms may be added to the agreement so long as they do not breach any provisions of the residential tenancy laws. Any such terms are binding or enforceable, if the tenant has signed the agreement.