Ulaa the Uxie:

Pronounced 'Yoo-Lah'

Mostly known for being 'The being of Knowledge', they are also associated with good health and healing, harvest, and the element of thunder/lighting.

Ulaa is a soft-spoken individual with a gentle nature and a fondness for mortals, be they human or average Pokemon.
They rarely open their eyes and often speak in a slow drawl as if always tired.

Stories told to children by elders from Solaceon Town say that Ulaa is like this from having accidentally eaten fruit from the celestial world that causes them to always fall asleep, but it is unknown if this is actually the truth or not.

Though genderless like most other legendary beings, most mortals use they/them and /she/her pronouns when referring to them.

 

Ravaa the Mesprit:

Pronounced 'Rah-Vaah'

Known as 'The being of Emotion', and for good reason, but they are also associated with the element of fire, lust/sexual intimacy, and wealth.

Ravaa is loud, extroverted, and boisterous in nature, and at times, quite selfish and childish. They are very fond of wine and alcohol.

Despite being associated with the element of fire (mostly for their fiery temper), Ravaa is actually no longer able to wield the powers of fire simply because it was taken away from them by their elder sibling, Duvaa, as a punishment for misusing their abilities in the past and setting an entire forest ablaze.

It is not uncommon to see Ravaa pestering Duvaa to return their powers of the flame to them only to be immediately denied or ignored completely.

Ravaa is genderless but others have often used she/her and they/them pronouns to describe them.

 

Duvaa the Azelf:

Pronounced 'Dew-Vaah'

Known as 'The being of Willpower', but is also associated with the hunt, balance, and of the elements of rain/water.

The eldest of the Lake guardian siblings, Duvaa is a very straight-forward and responsible individual, yet they tend to speak in a rather monotone and almost 'robotic' sort of manner.

They don't anger very easily (But WILL retaliate with deadly force if they feel themselves threatened) and are the least likely to smile or laugh.

Their body is small, but their voice is often described as deep and somewhat intimidating to others. Alongside that, their voice is also described as male and female combined, despite being genderless.

They are physically the strongest out of the trio.

He/him and they/them pronouns have been used to describe Duvaa.

 

Bonus folklore:

Legends from Celestic Town claim that the Fire, Water, and Thunder evolutionary stones are somehow connected to the Lake trio.

Whether this is true or not is not exactly known.
It's believed that this legend was created simply to have an explanation for the drastic biological changes for the Pokemon, Vaporeon.

As regardless of what its biological sex is an Eevee,
will always become a hermaphrodite once it evolves into a Vaporeon, further connecting the peculiar occurrence to Duvaa's intersex voice.