Eris has three siblings in ERIS (Eternal Truths, Book 1). I already mentioned in LKF #4 that the next Eternal Truths book would not be about Kaylie, Eris’s younger sister. I also mentioned in that post, as an aside, that Kaylie would get a book of her own. That book is planned, plotted, and just needs to be written. Her book will go more into depth about the family reunion dinner I glossed over in ERIS.
Eris has two other siblings — Benkei and Declan. Benkei will not have a book of his own. He will make a few cameo appearances in other books, but his story is pretty much told in ERIS.
Declan and Jarl (another mainstream menage, m/m/f this time) have a very interesting story that is part of another series I hope to start in two years, possibly three. It all depends on my writing schedule and how fast I finish the books I have planned ahead of it.