Please excuse any typos since I'm travelling and on my phone.
The Ebony Order is eager but not insane - theres no way they could take out the entire family in one night considering how powerful the noble magi are and how small the Order is currently. The Emperor is old but considered the most powerful magi in the empire, so hope of actually taking (just) him out is slim already. Sabrina. An attempt alone could bring them fame. The Ebony Orders goals are meant to be long term, not a single thread/event otherwise its over too quickly and theres no substance to enjoy. This event is meant as an introduction of their order to our canon and possibly major players in the story.
As far as the Emperors family tree
Cassius (NPC) - The Emperor
Alistair (PC) - Eldest Son (33) and *rightful* heir but his claim to the throne is in jeopardy. Some no longer consider him the heir.
Lilth (PC) - a twin and only daughter (18)
Tybalt (PC) - (23) son in law/Lilith's husband approved by the nobility (well...some)
Unamed brother (NPC currently) - twin and youngest son (18)
Because this is the first event of this kind, I want to reiterate that this event and the site in general is not about PvP. Even when characters are opposing one another in-character this is meant to be a cooperative storytelling experience. While one no one has crossed any lines, some talk here and in discord feels like it's trending in a more competitive direction so I thought it better to say something now. If we start to see people arguing, it will be dealt with quickly. We have pretty lax limitations on things like power levels, not so you can use them to win but to tell interesting stories.
There may be consequences to a character's actions in threads but no one will ever be forced into things like character death.
tl;dr - Work together to make a good story and stop trying to "win"
Kharia has used one hand to call down a series of random lightning strikes to create a lightning wall of sorts. This is to prevent Catrina from escaping via the window. Almost immediately after, she raised her other hand and sent streams of electricity toward her with the intent to render her unconscious.