I have enjoyed this story very much, but I think you may have made a little mistake with:
[ "Cissy is my biological mother, even though she never carried me, which will make Harry your uncle by marriage." ]
If Cissy is Narcissa mother that make Harry her Step-Father, and Step-Uncle. Severus's Step-Father-in-Law, and Draco's Step-Grandfather.
It also make Harry Step-Uncle-in-Law to Severus, and Step-Great Uncle to Draco though Bella. Also Bellatrix's Father-in-Law and Step-Uncle.
All by marriage to Cissy and Bella.
Author's response
Man, I can’t believe I missed that. This is why everyone should have a beta-proofreader, by now you’ve probably seen the chapter re-posted with the correction you’ve pointed out. I plan to use the Uncle aspect in a later chapter.
Thanx again,
N!