There are demands from the Count clans that might be materially feasible, but not culturally too. Everything that touches the nomads could go either way, and the demands of the Luo in particular could cause a significant cultural clash if we don't frame them correctly.
At this point, I strongly doubt that any side will unknowingly trample over some terrible cultural taboo. That's why and don't see much point in studying their culture even further at this point in time.
The important part is that everyone behaves in a polite and professional manner. As long as the will to actually reach and agreement is there, minor cultural frictions won't matter as much, specially if we smooth them over.
Besides, it isn't as if any culture is unaware of the concept of political marriages. Jaromila herself is married to Cloud Nomad Khan, so it's hardly going to be taken as an insult or some cruel act to the one being married off.
I do want to search for an alternative, though.
The scope of culture and history's relevance is being underestimated a bit here, I think. Obviously, it's relevant for avoiding faux pas, but it also goes beyond that. Avoiding mistakes would be the only utility if we assumed everyone in attendance wants the summit to work out, but that's a dangerous assumption. Some might be against it, some might be indifferent. And cultural values or ideology plays a huge part in this. We've seen a sample of this on our own side with the Diao; we opened with a pitch that offended their sensibilities. Not their material or organizational sensibilities, but their cultural and historical ones.
The most vital resource for the summit's success, the first step we can't miss, is fundamental legitimacy. We need to convince the parties arrayed that the other parties present are people(!) who are Civilized™️(!!) enough to bother entertaining the notion that a deal of any kind might be struck(!!!) and held to(!!!!). This isn't something we can take for granted, and we will need to work for it. The Other has deep roots. Our talk with Grydja exposed some of the more fundamental faults between our peoples, now we need to work on developing the kit to bridge them.
Lines on the map and other practicalities are obviously also very important, but remember that this is a first contact mission, and those lines on the map do not actually touch as yet. We've been to their northernmost holdings, they aren't close. Exchange of dialogue and basic custom comes before dividing the substance of the expanse between us. Necessity before comfort, even as we pursue both.
I think you are underestimating the progress we have already done in that regard, as well as the importance of material benefit to keep peace.
Sadly, just considering the other party "civilized people" isn't nearly enough to avoid the nightmares we saw in the Dream with Xuan Shi. If there is a gain to be made or riches and land to acquire, there will always an excuse to get them, even through conquest. Being aware that the other side aren't barbarians and can uphold a deal isn't enough to avoid that result.
The very fact that this summit is taking place proves that both sides are willing to give it a shot. In order to prove that a deal can be uphold, a deal has to be made at all. IMO, and it seems this is where we disagree, material concerns are going to be the decisive factor.
Besides, presenting the WS's demands in an acceptable manner it's also important to get the Empire to think of the WS as civilized. If the Count representatives think their demands are too egregious, they will conclude they are greedy barbarians you can't reason with.
We have to convince people on both factions that reaching a pact is more beneficial than war and conquest. If some sides think the agreement doesn't benefit them as much as they want or "deserve" the whole thing will fall apart.
That's why we need a clear understanding of what everyone wants or expect to get out of the summit. Again, we don't know what the WS wants.
It's precisely because our frontiers aren't touching that the cultural points of conflict aren't so relevant. For a long time, the ES isn't going to interact with the WS outside of trade, military collaboration and other things of such nature. Even if aspects of each other's culture seem weird or distateful, it won't really affect proceedings.
During that time, the ES and WS will interact and mingle, and thus they will get to know and understand each other's cultures.