So my friend posted this thing and I was like, guys, there are already tons of books like this? Then my stupid internet browser at work ate my comment, so here I am!
Okay so:
First, specific recommendations based on the above, and then just general “look, fantasy books that are doing the damn thing.”
Mermaids in wheelchairs:
- Deadshifted by Cassie Alexander (Edie Spence #4). The character is actually a siren, if I remember correctly, but she has a tail. This is the least exciting book in the series in my opinion. The first book is about a night nurse in a supernatural ER ward. There are shifters and vampires and mysterious multidimensional entities, oh my!
- One Salt Sea (October Daye #5) by Seanan McGuire. See below for the first book in the series. **added 01/12/18
Sirens using sign language:
- High Demon and First Ordinance series by Connie Suttle. The characters are by and large villains in this universe, but there is one in particular whose vocal cords were damaged intentionally and he uses telepathy and sign language to communicate. Trigger warning: Suttle’s books contain a lot of violence and misogyny and her characters are largely disempowered women with massive trauma issues. Many attain power and status and resolution later, but it didn’t sit well with me.
Religious vampires:
- Blood Rights (House of Comarré series #1) by Kristen Painter has a vampire named Preacher who lives in a church.
- In the Forests of the Night by Amelia Atwater-Rhodes also has several characters who have to reconcile their religion and their vampirism. There are honestly so many more but these are the ones that immediately came to mind.
Disabled fairies fighting for accessibility:
- The Hollows series by Kim Harrison. The pixies in these books have to fight for fair wages and anti discrimination. Also Jenks is just an all around fun character.
- Rosemary and Rue (October Daye series #1) by Seanan MacGuire also deals with this, delving even more into drug abuse, and racism.
- A Kiss of Shadows (Merry Gentry #1) by Laurell K. Hamilton. Although in this series the fairies are disabled mostly as a direct result of violence inflicted on them by a twisted and sadistic society or three.
Spirits fighting fires and saving people from natural disasters/situations that are too dangerous for the living:
- Glass Houses (The Morganville Vampires series #1) by Rachel Caine.
- The Name of the Star by Maureen Johnson (though more so as the series progresses).
- Grave Witch by Kalayna Price. The ghosts in this series are more bidden than selfless, but they are present!
- Shadowland (The Mediator series #1) by Meg Cabot. Kind of. Again, more bidden and subjective rather than a ghostly task force.
Fae snatching children from abusive homes while changelings wreak havoc:
- Seanan MacGuire again, October Daye.
- Trailer Park Fae (Gallow and Ragged series #1), by Lilith Saintcrow. This series is so so so good!
Liberated genies using their powers to fight for human rights:
- Oracle’s Moon by Thea Harrison. This is a romance novel and doesn’t have much plot to speak of. Mostly the Djinn is just horrified at the poverty this hot witch is suffering through, but I like this series, each of which can be read as standalone novels.
Psychic doctors, psychologists, teachers, etc:
- Calderon’s Fury (Codex Alera series #1) by Jim Butcher. All of the healers in this world are also empaths.
This is actually a really common element in urban fantasy, so it’s very odd that I am otherwise drawing a blank.
I didn’t get into a couple of the suggestions: shapeshifters with stretch marks is weirdly specific and I’m positive there are hirsute female shapeshifter protagonists with normal, stretch-marked bodies, but it isn’t treated as a point of contention or mentioned. Let me know in the comments if I mentioned any of your favorite, or if there are any I should check out!
I’ll leave you with a strong, genre subverting recommendation which is an awesome, 5 star read: 
In Other Lands, by Sarah Rees Brennan. Excerpt:
“What’s your name?”
“Serene.”
“Serena?” Elliot asked.
“Serene,” said Serene. “My full name is Serene-Heart-in-the-Chaos-of-Battle.”
Elliot’s mouth fell open. “That is badass.”
The Borderlands aren’t like anywhere else. Don’t try to smuggle a phone or any other piece of technology over the wall that marks the Border—unless you enjoy a fireworks display in your backpack. (Ballpoint pens are okay.) There are elves, harpies, and—best of all as far as Elliot is concerned—mermaids.
Elliot? Who’s Elliot? Elliot is thirteen years old. He’s smart and just a tiny bit obnoxious. Sometimes more than a tiny bit. When his class goes on a field trip and he can see a wall that no one else can see, he is given the chance to go to school in the Borderlands.
It turns out that on the other side of the wall, classes involve a lot more weaponry and fitness training and fewer mermaids than he expected. On the other hand, there’s Serene-Heart-in-the-Chaos-of-Battle, an elven warrior who is more beautiful than anyone Elliot has ever seen, and then there’s her human friend Luke: sunny, blond, and annoyingly likeable. There are lots of interesting books. There’s even the chance Elliot might be able to change the world.
