Thank you so much for giving me the opportunity to read your book. Please, keep in mind that my reading of your story is by necessity a subjective opinion. Your story is beautiful and important to you more than any other story you could have been telling. How I perceived it is very much a matter of my preferences.
I read the whole story because--spoiler alert!--I loved it so much!
Your book is tagged as historical, regency and mystery, so I looked first and foremost at how much the story immersed me in the world of yestereve, gave me a feel of problems that took me away from the modern world and character drama.
Your tags have a nice variety to them with a mix of genre, subgenre, mood and the specials the story serves, though young adult and medieval tag seemed out of place. Regency and Victorian are also two completely different periods (more on that later) and I would strongly suggest that you anchor your story in one of them. I would also suggest a tag like dotting-brothers or brothers because it is a popular trope.
Your blurb is spot on for a society romance. However, as much as I rarely comment on the covers, the cover in my view is off. Society romances have that codified expectation of a bright, dress-up cover, so I would encourage you to look for something in this style for your series.
I started with saying how much I loved your book, and it is an understatement. I truly enjoyed the whimsy and the mystery integrated into the society romance. I also could clearly see how this book is a foundational stone for the series. That takes a special foresight to do so. For example, when the younger daughter, Phillipa, is mentioned to drive her governess to tears, I foresee that one of the books in the series will have a Bronte-style governess who would scandalously capture one of the titled brothers' heart. Not going to lie, I am looking forward to that!
Your choice of the foundational value for your main character, Elizabeth, is fantastic. The family comes across as incredible, something we all only wish we could be a part of. Elizabeth also understands her strengths well and is an active plot-mover, without leaving a realm of believable. She is capable and she has just a touch of a drama queen in her and that's wonderful.
The mystery of the amnesiac John is fun and is tied to the society narrative of the romance. However, it takes Thomas to make it interesting for me, since John himself feels a little bland. After Thomas showed up, you kept me continuously engaged in the mystery, guessing who John might be, searching for clues. For me, however, your decision not to resolve the mystery in the same book that set it up, detracted from the plot.
Thomas is probably the most intriguing character in the male cast. I hope he proves to be a romantic interest for one of the brothers. Matchmaking is an exciting trope and your book invites to indulge into it.
One of the things I appreciated the most is the variety of relationships between the large female cast. There are catty attitudes of the rivals, there is familial attachment to older women and to a younger sister, and, in chapter 13, a female friendship with someone of Elizabth's own age. This spectrum helps create a rich world of women.
My suggestions below do not in any way suggest that I didn't enjoy your book. They are simply for your consideration if you decide to edit.
It is a matter of personal preference, but I would love to see your story anchored in where and when more obviously. My feeling was that this is a bit later period than Regency or Georgian, maybe Victorian or even Edwardian. In each of those time periods you will have all the trappings of the high society novel: titles, beautiful dresses, scandals and country estates. Such anchoring will help you create a little bit of a fabric of the society backdrop.
In terms of set up, in the first 2 chapters you repeat the routine of 'Someone is sick, quick! Send the footman to fetch the doctor!' twice. While calling in a doctor for the cook's child shows Elizabeth in a good light, the cook and her child don't play a role (in a book with a lot of characters); Elizabeth is shown to be capable/immersed into running the manor time and again; and it delays the fateful appearance by John--the seed from which the conflict of the entire story grows. Hence, I suggest eliminating the cook's episode.
For quite a while in the book, Elizabeth's brothers fell into two guys for me, Bart-Simon-Vincent and Matt. I had an impression that you need Bart-Simon-Vincent for the series rather than for this specific book. There is something you do in Chapter 12, when Elizabeth simply compares her brothers to animals--chameleon, dog, weasel--that would help in my view if you moved it into introduction. Another potential solution is to use a plot device to mention Bart, but send him away to do his studies or a Grand Tour, so Vincent may have more screen time and have more opportunities for character development. When times come for Bart to step on the stage during the series progression, the spotlight could be on him during his return and it would make the character more memorable.
Because the setting wasn't clear to me, I was feeling like a couple of background plot points remained nebulous. They are: why in 4 years on the dating scene in the countryside Elizabeth never met 3 of her suitors (even though one of them knows Rosemary) and the circumstances of her parents' death that are only very briefly/vaguely related. Defining a historic period might help you find a more specific way to get rid of her parents.
Good luck with developing your series and hope these notes are helpful!
