Stop making me ship them! XD
Okay, back to the critique part of the job:
The style really resemble horses, the body lines, etc. I love how you made Twilight look more slim than Tempest: her shoulder looks skinnier than Tempest, the throat latch, the chin... It points out and gives the impression of royalty, that Twilight isn't as strong (at least physically) than Tempest and it looks amazing!
Tempest on the other hand has some very strong lines, implying she's buff
and combat-ready (if that even makes sense)
I love the wings! Looks like bird wings! That's attention to detail! But not any bird wing, looks like a bald eagle wing from the lesser and median coverts! Wonderful!
In Tempest skin you can see some scratches, some battle damage, in contrast with the slim Twilight's skin, another point for buff
The manes too are another great detail: Twilight cares for her mane, because royal reasons and such, although Tempest's don't follow a particular pattern, isn't linear, implying too some battle and buff
She's like: I don't have time to care for myself, I need to be ready at all times, have to be at my post.
Twilight's horn too is another great detail: looks more thin and slim in the base that Tempest's horn, that's so cool!
I don't know what else to say here, but amazing art, my friend! Really wonderful details and expressions! I absolutely love it!!
And now I ship'em!