Advice for Changes to CoS

Hi!!! So I'm a new (not brand new, but close) DM running CoS for three brand new players. My players have requested no necrophilia or incest so I've had to make a few changes to the game. I'm struggling a little bit with this and tying in my character's backstories.

The necrophilia: I'm pretty sure the instance of this is Fiona Watcher's husband. I know it's important to her character because it's one of her dirty secrets, so I was trying to find a way to give her that secret while having her husband be buried. I think the way to do this is Stella. At first I was going to just have had Lady Watcher have been responsible for her insanity instead of Victor, but then I had a better idea.

One of my characters is an orphan, and I was thinking I could have Stella be 'missing', ie. Lady Watcher bargained with Strahd to let her live in the outside world where her mind could heal. In this scenario, the mind-fracture would have happened a lot younger (eight or so) the player would have no memories before that age. Is this even a good idea? I was inspired by Mandy Mod's idea to make a sibling for Izek Stranzi, but I was worried about taking the sadistic edge away from him and lowering the Baron's cruelty level. If y'all think Stella's a bad idea, then that's my back-up plan.

For the incest, I was already planning on reworking the mongrelfolk as I don't love their depiction of mental health issues, but I just want to make sure that that's the only instance of that in the book.

Finally, I have another player with a plot hook. Their character made a deal with a powerful being of some sort to exchange their eye for their sibling's (heal their sibling. I've determined this is 7th level Restoration with a blood cost) and I'm think yay! dark power time. Problem, I have literally no idea how to work this into my campaign, and I'm not sure I like the idea at all. Should I have the power show up? Tempt them with more deals? Not make it a dark power but make it a figure of equivalence to an arch fey who has a stake in seeing the planes rise or fall?

I also have a third player whose backstory I currently have no hook for, and I'm worried about them feeling left out. That player is a Golaith TN in pursuit of knowledge at all costs, and I'm thinking maybe have an incident in their past where the player did a bad act for knowledge that was pre-meditated by a dark power? I have no idea.

Any advice welcome!