two sisters lose their parents in an auto accident, the eldest sister has a secret that will bring turmoil to the family.

One thing; having a secret does not bring turmoil, revealing the secret is what will bring turmoil.
And if revealing the secret is what causes the turmoil in your story, (not the auto accident) then it's probably the inciting incident, and I would lead with that in the logline.

Who is the lead character
What is their goal
What is standing in the way of their goal