Would this description set the hook?

[Guy]

Potential description for my novel for the back cover. Need constructive feedback. Thanks in advance.

According to legend, this wasn’t supposed to happen. By conventional wisdom, their existence is an aberration
The Chosen are seldom born, and for more than one to exist at once was unheard of and said to be a portent of disaster. Yet three of them are born on the same day. Aleena is a warrior whose greatest desire is to be left alone, yet she cannot avoid the responsibility the gods gave her. Anlon is a warrior whose greatest desire is to prove his worth. Believing they are the only two of their kind, they crave each other’s companionship while recognizing their potential rivalry. Both are gifted and skilled, proud and jealous. Both also face the same decisions, yet each makes a different choice, setting in motion events that may well bring about the disaster the legend speaks of.
But there is also a third Chosen, a witch whose greatest desire is to find peace with herself and discovering where she stands with her fellow Chosen. Her decision can either ensure disaster occurs, or it can usher in a new era for these rarest of mortals, the Chosen.

 

[Steerpike]

No. for me it would not. First, I don't find the writing engaging. Nothing here excites me about the book. Second, I think you probably give away too much here. Talking about two characters craving each other's companionship while recognizing potential rivalry is something I'd like to learn about the characters over the course of the book, not find out because the back cover told me.

Spoiler-type stuff is a big reason I don't generally read back covers in the first place, but if I did read this one there is nothing here that would make me likely to buy the book. It's very flat.

 

[Guy]

Yeah, this is probably my biggest Achilles' heel in writing, so I could really use some help. It could be worse, though. I could start off with the phrase, "In a world..."

Let's try this one:

What wasn’t supposed to happen, happened. The rarest of mortals, the Chosen, are seldom born, and for three to live at once is unprecedented and said to lead to… interesting times. Aleena struggles to come to terms with her gift, as Anlon struggles to control his. Both are gifted and skilled, proud and jealous. Their rivalry is inevitable, yet Aleena knows Anlon is a brother in addition to a rival. Her love overcomes her jealousy and she shows him mercy. For that, he will never forgive her. His obsession for vengeance threatens to consume all she loves.
Yet there is a third Chosen, a witch quietly watching the other two. With Aleena and Anlon sparking interesting times, how does the witch factor into the equation? Does she balance it and restore order, or does she unbalance it into further madness?

 

[Devor]

I'm moving this to Marketing - Cover Design is more about the artwork. Your blurb is a marketing tool.

In general you want to zero in as much as possible on the character, and tell the first part of that character's arc in the abstract. You're kind of doing that in a passive, roundabout way. Abstract doesn't mean passive. The same rules for writing still apply, just with ideas instead of things.

 

[A. E. Lowan]

Yeah, this is probably my biggest Achilles' heel in writing, so I could really use some help. It could be worse, though. I could start off with the phrase, "In a world..."

Let's try this one:

What wasn’t supposed to happen, happened. The rarest of mortals, the Chosen, are seldom born, and for three to live at once is unprecedented and said to lead to… interesting times. Aleena struggles to come to terms with her gift, as Anlon struggles to control his. Both are gifted and skilled, proud and jealous. Their rivalry is inevitable, yet Aleena knows Anlon is a brother in addition to a rival. Her love overcomes her jealousy and she shows him mercy. For that, he will never forgive her. His obsession for vengeance threatens to consume all she loves.
Yet there is a third Chosen, a witch quietly watching the other two. With Aleena and Anlon sparking interesting times, how does the witch factor into the equation? Does she balance it and restore order, or does she unbalance it into further madness?

You use the phrase "interesting times" twice. First, don't repeat phrases - unless they have significant thematic meaning. Second, I'm sure you're referring to the old Chinese curse, but since I imagine your world is not Chinese you may want to go with another pair of descriptive phrases. Take out your periods of ellipsis. Dedicate one punchy sentence to each character. Example - Aleena struggles to come to terms with her gift. Anlon struggles to control his. (Might want to change up the word "struggles," here.)

Keep working at it. You're getting warmer with each try.

 

[Chilari]

Your blurb is still a bit spoilery, at least in terms of the character relationships, while failing to reveal enough that actually has the potential to hook. What's the core conflict? Don't put that in, put in the symptoms of it. Why is it bad to have three Chosen alive at once? What's going to happen? Again, don't reveal the ending, but do consider alluding heavily to a major event that happens in the first quarter of the book.

Be briefer in your characters. Characters are good and important to include, yes, but explaining the rivalry between Aleena and Anlon in such detail looks like it's taken straight from your novel notes. As Steerpike said, you can reveal their rivalry in the book itself. In the blurb, only hint at it, if you mention it at all. Try something like:

Aleena just wants to be left alone, but her rare gift pushes her to take charge. Anlon struggles with obsession and jealousy when he discovers he's not as unique as he believed.

Add in the core conflict and inciting event, then the witch twist at the end, perhaps changing the tone a little to be less vague and include a personal conflict the witch must overcome, like with Aleena and Anlon as I've written above.