OOOOH BOY DO I HAVE BOOK RECS!!
it's not quite fantasy, def more sci fi, but there are sea monsters? scientifically created sea monsters. and lesbian pirates. its called The Abyss Surrounds Us by Emily Skrutskie (and the sequel, The Edge of the Abyss)
a sci fi rec: do you love aliens? do you love found family? do you love well-developed characters? The Long Way to a Small Angry Planet by Becky Chambers has all of them! As well as a character that uses they/them (not quite in a nonbinary way but it's there), two wlw, one of the characters has two dads. a character-driven book rather than plot-driven so it seems kind of slow BUT this is one of my all time faves...
if you end up enjoying The Long Way, there's two more books in the series about different characters. A Closed and Common Orbit is about an AI learning to exist in society and not in a ship, as well as a young version of another character escaping her horrible home planet. There's a genderfluid character, which is the only explicit LGBT rep in this one but I adore this book. this is also quite character-driven but theres also a really intruiging plot
Record of a Spaceborn Few is the latest book in the series. I haven't finished it yet, but there are old married lesbians and i love them and maybe more rep, I'm only like 25% in the book. This is about several people aboard the Exodan Fleet, a group of human-occupied ships. I'm missing the colorful casts of aliens but it's shaping up to be another great book.
The Miseducation of Cameron Post by Emily M. Danforth (realistic fiction) is SUCH a good book but also there's not a very happy ending and there's a lot of homophobia (cameron post gets sent to conversion therapy) and a description of self mutilation (not too too descriptive but i reaaally didnt enjoy it). also some mature content. but i LOVED this book. also there's a movie of it which i've heard is also very good! there's lots and lots of wlw, a two-spirit character, and it's quite a long book if that's what you like.
We Are Okay by Nina LaCour (realistic fiction) is a wonderful, somewhat confusing book. One of my all time faves. It's about the reconnection of friends after one of them loses her grandfather (who was her only family) and discovers secrets he's been hiding. There are flashback-esque chapters that reveal said secrets over time. The main character is a wlw. God i love this book.
Simon vs. the Homo Sapiens Agenda by Becky Albertalli (realistic fiction) is about emails between two gay boys and how they end up falling in love. I'm a wlw so i can't vouch for everything Simon goes through but it's a fantastic book with great characters and accurately shows struggles of lgbt people. A really sweet book I love it.
Leah on the Offbeat by Becky Albertalli is the sequel to Simon vs. This one focuses on Leah, Simon's best friend who is bi. Another really good book and I'm not bi so i can't vouch for Everything leah goes through but its Really Good. i love it. so good.
finally some actual fantasy suggestions... Six of Crows by Leigh Bardugo and the sequel Crooked Kingdom. There's some bi rep and it's not a big thing at all but these books are. So Good. It's about some criminals who have to pull off an impossible heist, and ughguhughg its so good. There's magic and that's the fantasy part.
Not Your Sidekick and the rest of the series by C. B. Lee is a superhero book about. people with superpowers, which is a normal thing in this universe. The main character is the daughter of two superheros. A few wlw as well as a trans character; i havent read past Not Your Sidekick so there could be more.
Radio Silence by Alice Oseman (realistic fiction) is another GREAT book about a fan of a podcast who starts working with the podcast but things start to get out of hand. Main character is bi i think i forget. Mlm side characters, god love this book.
If you're a fan of comics the Runaways comics are wonderful. They're Marvel comics so fantasy in the superpowers sense. A big found family, wonderful characters, and the newest run that started in 2017 is absolutely awesome! There's a good deal of wlw and a genderfluid character.
The Rest of Us Just Live Here by Patrick Ness is fantasy because there's some fantasy elements but this book focuses on the people who aren't part of the Big Narrative, so it reads more like a realistic fiction novel. There's a gay boy and I haven't reread this in a long time but I loved it so much and its really, really good.
My last rec is It's Not Like It's A Secret by Misa Sugiura (realistic fiction) which is about a girl moving to a new city and trying to fit in and also falling in love except its Complicated tm. The main romance is between two girls, lots of poc rep, a good read!