A lot of good points brought up; Sharpe's, Gruchak's, and Melissa's all ringing most true. That last line might work good as a hook; consider playing with it.
Sharpe has the best point about the book's size; you need to decide what it is first. Is it a quarter million word epic? Then leave it as it is. Don't mention splitting it. The agent and/or publisher will talk to you about that if they think it's appropriate. Otherwise, decide on the splitting points and the volume titles before you start querying. You might be best suited querying it first as the full-size epic - both to agents and publishers, per Breyer's suggestion - and if that doesn't work, let it wait a month or two before trying again after splitting it into volumes. Do one or the other, and leave it to the publisher and/or agent to decide on splitting or combining later.
You mention, though, that it's still WIP; careful putting together a query before you've done extensive revisions. It's not that you're jumping the gun, but you run the risk of omitting scenes added during revision, or referencing ones that are deleted, or whose tenor has changed in editing.
Now, to launch my Wall of Text Assault...
Cadell knows nothing of black-elves until he witnesses a band of them stumble through a rift into Faerie. His best friend falls to their iron weapons despite a human mage's attempt to heal him. When Cadell kidnaps and tortures the mage in grief-driven vengeance, the mage's family and four light-elven allies rescue him.
This reads off like a list of facts without much panache to them. Simply start out that he's attacked by black elves, tortures one, and then... something happens. I say something because the wording is slightly unclear. The black elves have light elven allies? And the grammar of "rescue him" actually can imply that they rescue Cadell from the elf he's torturing. It would be clearer to state that Cadell tortures the mage, until the sorcerer's family arrives with allies and frees the black elf. English can be very bad about being very vague if you're not careful.
And while this sets up events to unfold, it can be condensed and told more concisely; it isn't the most important part of the story.
Though the rift between realms is shut, the light-elves fear another may open. More black-elves appearing would endanger mortals, immortals and wildlife alike.
There's no mention of how nor why the rift is shut. The second line is also a bit redundant; it can be implied already that they're a threat, and that more of them pouring through a rift would be a bad thing. The line adds nothing to the query's purpose, really, which is to state the facts of the book and let the agent see what it's about; it's just an empty flourish.
Seeing no other option, Cadell surprises himself and suggests the unheard-of: an alliance between Fae and humans (and light-elves by proxy). To everyone's surprise, his queen agrees, and negotiates a temporary truce.
This feels like it can be simplified down into one thought, and stated a bit more concisely. I know you've got a lot to pack in, so it'll have to be summarized to get the story's full plot into focus; state that he only comes up with the option, and the queen goes against the expected norm and agrees.
The light-elves' fears are soon confirmed. A spy comes through a second rift, and kidnaps Cadell to the black-elves' caverns. When the black-elves torture Cadell, he recognizes and despises both his people's cruelty and his own, and resolves to change his ways. With aid from an unexpected ally, he escapes to tell his queen of the black-elves' ruler: a sorceress known as the Lady.
This is where the query should be coming to life, but is reading off like a list of events, instead of a flowing series of them. The first sentence is a bit superfluous and can be combined as a more concise, smooth observation in conjunction with the spy's arrival and Cadell's kidnapping. We can assume that he's taken back to the black elves' place across the rift, but only if you also state that the spy is a black elf himself; right now he's just "A spy". The about-face he makes during his torture is a little abrupt as stated; how is he reexamining his life? Is his torture making him realize the pain he's been dealing out?
At any rate, it's sudden and without description; let us see his conflict and the journey he takes to his new lifeview.
The unexpected ally is also unnamed; who is he or she? How important are they to the story? It might not be necessary to name them, but how unlikely is this ally? Is it a black elf? A light elf? A human? It could be a houseplant for all we're told (not being cruel, it's just the first thing that came to my tired, twisted mind ).
It's also a little unclear how important it is that he tell his queen of the other queen's identity. Other than giving what I presume to be the main heavy a name, it doesn't serve any other purpose.
As the allies anticipate war, Cadell begins his own battle.
Anticipate or prepare for? "So be it - Threaten no more - To secure peace is - To prepare for war"
...Sorry, couldn't help dropping the Metallica line. Excuse me while I riff for a moment.
But there is a difference, grammatically. Actively arming and recruiting is to prepare for it, while anticipating means that you're either already ready and just need for it to start, or you're going to do nothing and let the opposing army roll over you. "Arming for" could be another, perhaps more precise term if that's what they're doing.
He shuns his people's stagnant, selfish ways, craving adaptation and a lasting alliance with humans for survival's sake. But not everyone wants Cadell's voice to be heard.
A cryptic line. I don't think it would hurt the query to state who these factions are that want him silenced and for what reasons; are they opposed to new ways of thinking? Or are they addicted to the war? It would likely intensify the stakes of what I think is the primary conflict here: Cadell's war with himself.
His revolution's fire may leave his life in ashes, if the Lady and her horde don't kill him first.
This might be best served as a hook, or the basis for a hook. The previous lines - worded more intensely - could provide a strong way to finish the query off.
There's promise here, but as stated, it feels like a lot's missing. I didn't attack this one as deeply as I could because it's still a work in progress and the manuscript isn't finished.
As I recommended for Whik's query, you might actually consider at some point writing out the full synopsis first - a full one, line by line, sitting at a ludicrous number like 3000 words - and then pare it down from there for your actual synopsis. Then, it could provide you a base from which to work for your query's synopsis. Although you've got a lot of points of view, it could help focus you and pick out the most important details to the overall development of the plot and most primary character, who looks to be Cadell. Focus on him and how he affects the story, and the rest should fall into place. I don't envy the task, but it looks like you've got a strong base from which to start with.