I did a segment with just the Eisner family like...a month ago. So here’s the main lords and the Eisner twins!
Dimitri, Edelgard, and Claude met Byleth and Reus years before the trio’s time as students at the Officer’s Academy. It may or may have have involved crossover shenanigans, but I’ll leave it at that.
So while they do try to hide how exactly close they are at the Monastery (because…politics and also there would need to be explanations they don’t care to have).
The stress and nightmares and new traumas drive them to each other over those in their house, usually, especially because no one will ask. They find comfort in napping or cuddling together, and none of them dare ask when the question “can we have some quiet together?” is asked. It’s basically their safety phrase.
Dimitri and Edelgard are actually the ones most likely to seek someone out, if not everyone. With the Western Tragedy a huge trauma spot for Dimitri, and Edelgard’s torture and now TWSITD trying to put her back under the machinations, They Need Comforting People. (Yes I am referencing some stuff that changes in my fanon, feel free to ask about them). Edelgard almost never asks for the comfort when anyone else is around, but Dimitri is more blunt and will ask in front of people (though quietly). There were rumors that at least some of them are entangled romantically or sexually, but since these are really the only signs of such relationships the rumors die quickly.
They all have their own cuddle styles. Because of strength and weight concerns from Dimitri and Reus, respectively, they tend to be either at the bottom of a catlike pile or big spoon. Sometimes Dimitri pulls Reus on top of him because it’s nice to have something (or someone) who actually feels heavy with his strength.
Edelgard is actually a hugger. She grips whoever happens to be with her or closest to her in the cuddle pile. The pressure is comforting (and if she’s in a bad headspace, a hug is a very different feeling than anything that tore her flesh) and so she wraps herself around whoever she’s grabbed onto. Claude and Byleth are really the only ones who hug back tight, because neither are afraid of accidentally hurting Edelgard.
Reus strokes hair. He finds the softness comforting, and everyone else finds that he’s gentle and they’re happy to let him stroke their hair. Usually. Sometimes they’re not and they’ll be upfront about it.
Claude likes to be a layabout and just. Plop onto people. He thinks it’s hilarious and also he says everyone’s more comfortable than a good clearing of grass. He doesn’t like people’s hands on his back, so even when he’s hugging someone he’ll usually keep their hands to his sides or around his shoulders (“more my shoulders than my back,” he’ll laugh).
Byleth is very still, but very vigilant. She wants to protect this part of her family after everything. She’ll reciprocate whatever hug she’s receiving, but when everyone else falls asleep she’ll often be awake. Unless they’re all gathered at night, and then she might fall asleep.