Time for some consideration of our goals, I think.
We do want to be allied with both Chesna and Ezti. It's very much to our benefit to have people with a good opinion of us and with an interest in looking out for our interests as our neighbors, so it's important that whatever happens we maintain their goodwill. Fortunately we already have that by default, since we're related and both of them are seemingly friends with Dita, who is on our side at the moment.
Beyond that default, though, both of them have serious issues. Chesna is basically having her fief run by someone she seemingly dislikes and who definitely has his own interests at heart, has a thirst for adventure and the exotic that simply isn't being met, and doesn't have marriage prospects she both approves of and is capable of pursuing at the moment. Ezti's fief is openly hostile to a powerful, militarized neighbor. We need to discuss these issues with them and see what assistance we might be able to offer in resolving their problems, and what they'll be able to offer us in turn. Alliances are built and solidified on the groundwork of mutual benefit and assistance, and it's that which we need to try to build up.
Marriage is one thing that we might be able to use to our advantage, but marrying Ezti would immediately plunge us into a war that we don't yet have the assets in place to win, and marrying Chesna wouldn't be of anywhere near as much benefit to our prospects. That means that in order to move forward with either, we would need to work out with them how to pull it off successfully and maximize the gain to both parties. As we're spending days in close proximity to them, this is a prime opportunity to talk over just that, if as part of the topic of how we can assist each other- a marriage alliance is ultimately just another option on the table here, and while an important one it's not the only one.
Throwing a few ideas out:
-Assist Ezti by building up our forces and militarily allying with her against Rogatica.
-Assist Ezti by establishing friendly relations with Rogatica and feeding her information as to his assets and plans.
-Assist Ezti by arranging the assassination of Rogatica (do not mention this one, but think it and find out about his heirs, etc.).
-Assist Chesna by arranging for a confrontation with Nikolai in which he loses face and/or social standing, potentially including his position, or otherwise is forced into doing something she wants.
-Assist Chesna by helping her mother find her a suitable match, and attempting to push for someone who suits her preferences (and also ours) while doing so.
-Assist Chesna by convincing her mother of virtually anything that she wants her mother convinced of but is having trouble with, and a charming young lord she has at least some trust for might be listened to about.
-Chesna helps us by aiding us in getting leverage to force Nikolai to stop screwing our fief.
-Either of them helps us by having some of their troops or retainers come aid us in clearing out haunts, beastmen, bandits, or river pirates.
-Either of them assists us by arranging to purchase or otherwise acquire certain grimoires from Baron Timis.
-Either of them assists us by helping us to find a suitable wife (if we conclude that they themselves are off the table).
Essentially, the key point is to remember here that we aren't just talking to two lovely women that we might want to marry- we are talking to two allied nobles with whom we can and should be scheming. Some of the above might not be practical and certainly some are mutually exclusive, but the point is that we need to get some serious plans made while we have the chance to speak with our allies.
As far as flirting goes, remember the halo effect- if they think well of us in one area, they're likely to think well of us in other areas as well. That means it's to our benefit to banter up a storm and make them both enjoy our company and regard a great deal and crave more of it. We should go as far as we can without offending either of them in any way, giving the impression that we're actually promising anything, or doing anything potentially politically detrimental. Essentially, be willing to go as far as they're willing to go while making sure they understand that everything is being done purely for fun, and unless we hash out a serious alliance with all practical considerations taken into account nothing can turn serious. We don't need either of them feeling somehow deceived.