Most tenants will not start to look around for another place until the lease arrives in the mail. Then they will string you out as long as you will tolerate it by hanging on to the unsigned lease while shopping for somewhere else. A tenant with an unsigned lease has the leverage. Is there a reason why the tenants can not come to you and sign in your presence? If so, advise your tenant that they can avoid a rent increase if you receive the signed lease by X date.