i have 2 dependants over 19ys old. Do i need to add them to the dependent list ?

You can claim a dependent amount under certain conditions (their income isn't too high). It could also be useful for cases when you're paying for any of their school tuition.

Generally , its ok not to enter as dep. In some situations this may be advised to enter for example if you want to transfer tuition or dependant has any kind of disability