As one who was heavily considering making this kind of faction over a month ago I've got a recommendation to make.
Don't have Fel PCs. Or at least not from the ruling line. The reason for this is very simple. When you make a faction dependent upon the leadership of a single PC then the faction will only really go so far as that leader goes. This is not an indictment of you as a leader at all. I honestly do not know how you lead. What I do know is that people leave, life gets in the way, other commitments come up, and it can be hard to lead for an extended period of time in a very active fashion.
An NPC line of Fels frees you of this. It gives you consistent leadership to point to, flesh out a family tree and it gives more Fels for anyone to interact with. It also creates great opportunity to kill off the Emperor more freely for story, or kill members of the family in order to make for interesting story.