Dark romance, 3 males 1 female.. lost memory

Hey!! I dislike to come here and waste anybody’s time but I’ve been looking for a book series I read on kindle unlimited and can not find it no matter how many different ways I google it. I’m guessing it could’ve been an indie author and that’s why it’s not popping up. Anyways there’s a FMC & a MMC and I think the fmc sister was involved and that’s how she got back around to meeting the mmc, but there’s also smut with the 2 best friends but they’re not really looked at like best friends, because come to find out she’s lost her memory of the mmc and his friends and they are actually like a queen or king of hell? Please help if you can!!! I wanna say it was like 3 books (I’ve looked at my borrowed books and can’t find it through all my others)