Post-ITA Family History: Do I need to list estranged adult step-siblings and step-parents?

[Veeeera]

Hi everyone,

I’m currently filling out my post-ITA e-APR (Express Entry) and I’m hitting a gray area regarding the Family section. I want to make sure I don't trigger a rejection for misrepresentation, but I'm also dealing with a very disconnected family dynamic.
Here is my situation:

• My biological parents divorced when I was a child and I lived with my mother.
• After I turned 18 (but before I turned 22), both of my parents remarried their current spouses.
• I have never lived with these new spouses, nor have they ever provided me with any financial support.
• Neither of these new marriages produced new children, but both spouses have adult children from their previous marriages:
  • Father’s spouse has a son who is my age (30). He has never lived with my father either. I know his name and birth year.
  • Mother’s spouse has a daughter who lives abroad. None of us have ever met her, and I literally do not even know her name.

My questions for this situation:

1. Do I need to add my parents' current spouses as "step-parents" in the system, or do I just list my biological parents as "parents"?
2. Do I need to declare these two individuals as "step-siblings"? If so, how am I supposed to list my mother's step-daughter when I don't even know her name?
3. Is a Letter of Explanation (LoE) detailing this structure the best way to protect myself from misrepresentation?

Would love to hear from anyone who has had a similar complex family tree. Thanks in advance!