I read some speculation of conflict between the Twins in the future, so I thought I'd consider some practical issues regarding such a split...
First, the two bring pretty different things to the table; Jezera appears to be a talented mage and peerless spymaster (when she's not distracted by toying with her prey, enjoying her role too much, or bringing strays back to the castle instead of turning them into assets, at least), while Andras is a sexy shirtless god of war and natural-born leader (when he's not busy killing more of his army for "weakness" than the enemy, at least). At first, these appear to be fairly equal contributions... Except that as time goes on and their power grows, the value of a "sexy shirtless god of war" diminishes as you rely more on a real army instead of a single strong demon. His value as a leader remains, especially since many of your allies value a strong leader who can take to the field, but that doesn't necessarily have to be him; other, more pliable, figureheads can assume that role. The value of your teleporter/enchanter/spymaster remains consistent, however; until the war is won, you're always going to want to know what your enemies are up to, and be able to quickly respond. Thus, as time goes on, Jezera's value waxes, if anything, while Andras's wanes.
The two differ in costs, as well; Jezera's antics carry frequent delays and distractions, but they generally stay in the realm of delays and distractions - she annoys important allies and demands people waste their time amusing her, but she rarely blows up your plans or kills people you need alive, Dark Elves aside. Andras, by contrast, actively wants you sacking villages, and makes a point of slaughtering for fun, no matter how much value his victims offer. As time goes on, Jezera's costs are likely to diminish in aggregate as she can only play with so much of an ever-growing staff at once; Andras's costs will impede growth, but diminish as well - except in a diplomatic context, where his love of bloodshed will galvanize resistance.
Their influence on and value to the coalition thus far appears to change based on Rowan's actions; Delane seems to get along well with Jezera based on what we've seen, while Batri gets along with Andras. Patricia is loyal to both Twins (absent Rowan's scheming), while I suspect that Jacques takes more towards Jezera; he might consider her a rival player, but people like him tend to prefer rivals to dangerous elements that will upend the board on a dime. Raeve, naturally, is exclusively loyal to his master Jezera. Of course, all of this is assuming Rowan remains completely passive, which is unlikely.
In Bloodmeen itself, they have markedly different bases of support; Jezera commands the loyalty of the castle staff and Shaya; Andras, the Orcs, and Draith. The others might have their preferences, but I don't believe any of others would likely intervene in a struggle between them without a significant reason. Andras, if he acted quickly, could likely win a direct conflict; Jezera would almost certainly hear of any prolonged plot, however, and could likely have them all poisoned and/or killed in their sleep with a bit of preparation. Whoever strikes first would likely win, so long as both remain in the castle.
Setting aside such things as "It's neat to see two evil overlords actually cooperating for once instead of pointlessly betraying each other and losing everything", there would appear to be good reason to let Andras go as time goes on unless he shapes up, and Rowan can readily shape the situation to ease that transition. Cutting out Jezera does not appear as viable unless you enjoy the idea of walking everywhere should the portal malfunction (or start collapsing reality or somesuch) and learning to brainwash people yourself; it could be done, but the costs are notably higher, the apparent benefits slimmer, and she's more likely to catch wind of the plot.
$ change_actor_num_flag('Jane', 'Jezera_Influence', 3)