Credit to Umbra74 on DeviantArt. 

1. 

Name: Spiritus 

Alias: Saleos (Angel name), Lord of the Shadow Throne, and Shadow walker. 

Race: Angel (formerly), Demon

Gender: Male

Size: Large

Eyes: Blue 

Special features: Marks on his shoulders

Appearance: 

Affiliation: Heaven (formerly) Hell, himself

Occupation: Demon lord

Relative(s): Kronos (older twin brother)

Partner(s): Nova (former lover, deceased)

Enemies: Heaven, Mundus, Zeref, Acnologia, Salem, the Dark Rebel Army, and other enemies. 

Allies: Inanis (Abyssal creature), Samael, Vulgrim, Four Horsmen, and Fairy Tail.

Powers and abilities: 

Spiritus here is more mage type of demon. His primary defense and attacks is magic and primary elements are lightning and shadows. 

He will have a weapon but can't chose if his classic axe, sword or staff instead.

Biography: Spiritus, originaly named Saleos, was formerly a angel but was cast out of Heaven into a Hell for meddling with dark magics, mainly around shadow magic and necromancy. Thus he becomes a Fallen Angel. 

In time in Hell, Spiritus body change to be demon and no longer bearing any resemblance of angel. He also have a time studying more about shadow magic and manage to get access into Shadow realm. In Shadow realm he create his own domain know as Shadow Throne. Without a Mask of Shadows or any power shadow artifact, his domain change is structure at will making anyone easily be lost in labyrint, probably not even come back alive. His domain or his access to the Shadow realm is guarded by his brother Kronos, who was also an angel but he was willingly go with his brother, even though he didn't do nothing. 

He stay independent, not taking any deals of bargains from Mundus, Samael or others demon lords. Being a demon lord too, Spiritus is know for his silver tongue and one of few demons who don't actually lie, as most others do. He use cunning and magic over a brutal force. 

2. 

Name: Kronos 

Alias:  Rahab (Angel name), Gatekeeper to The Shadow Throne, and Ashbringer. 

Race: Angel (formerly), Demon

Gender: Male

Size: Large

Eyes: Yellow

Special features: Marks on his right shoulder, scar on chest, and upside down wings.

Appearance: 

Affiliation: Heaven (formerly), Hell, Spiritus

Occupation: Demon lord

Relative(s): Spiritus (younger twin brother)

Enemies: Heaven, Mundus,  Zeref, Acnologia, Salem, the Dark Rebel Army, and other enemies.

Allies: Inanis (Abyssal creature) Samael, Vulgrim, Four Horsmen, and Fairy Tail.

Powers and abilities: 

Kronos is warrior type of demon and gives him a more fire-ash color skin to match as fire demon, which is his primary element as most demons are. He holds a giant sword he named Ashbane.

Biography: Originaly named Rahab, he's Spiritus (formerly know as Saleos) older twin brother, and together they were servants of Heaven until the day when his brother was cast out for meddling with dark magics. 

Kronos willingly go with his brother, even he didn't committed any crimes against Creation. As many eons in Hell as Fallen angel, he starts losing any sign of Angel and soon he was make into the demon, like his brother. While his brother keeps study with shadow magic and even manage to access into Realm of Shadow, he keeps Spiritus in check, because sometimes he fall into madness to deeply.

He now serves as his brother's gatekeeper into his domain know as the Shadow Throne. Many call him as a honor demon for very few demons exist like him, maybe it's because a part of an Angel still reside in him. His precious honor is above all else, but it's more his brother he cares deeply.

I hope guys like these demon twin lords. How they will appear is up for you guys to decide. Let me know at the comments below, peace out and enjoy!