Yes, it is essential to tell it out. Because not letting them know affects in 2 ways one is Psychologically and one is Diabetically. Psychologically you can be stressed due to the guilt of hiding it which in turn can increase blood sugar. And Diabetically in the sense you cannot follow a right diet as your household members do not know your condition and will persuade you to take high calorie and glucose dense foods as well. So expressing it will also draw their help.