That's what Japanese entertainment is for.
You know what, OP. I've been reading some ecchi manga lately, and though I can't recommend anything about incestuous schizovampiric sisters (there's one about a loli vampire called "Blood Alone", though she's not your sister), there's one manga I think you might like, IF you're a weeaboo. If you're not a weeaboo then disregard.
It's called "Papa No Iukoto wo Kikinasai!" meaning "Listen to what Papa has to say!" or simply "Listen to Papa!".
The main character becomes the adoptive father of his 3 nieces, 2 of which are not related by blood and one of them has a crush on him and calls him "oniichan" instead of ojisan/uncle. MC is 19-20, the nieces are 14, 10 and 3. Panty shots, bath scenes, boobies. Pretty mild ecchi.
I downloaded it thinking it could serve as a fap material, but it also had the "tragedy" tag, which I foolishly ignored. A few chapters in and I'm already in tears. The youngest girl is super adorable and it's pretty heartbreaking to see her cry.
The manga ends after just 12 chapters, while the original light novel is still continuing (18 short volumes so far). There's also an anime, and the name of the studio in charge is, get this, Studio Feel.
https://en.wikipedia.org/w/index.php?title=Papakiki
https://bakabt.me/torrent/172469/papa-no-iukoto-wo-kikinasai-listen-to-me-girls-i-am-your-father