(I chose Iceland because my mind considered him to be most likely to suffer from insomnia.)
Denmark|Matthias Køhler: Matthias would be extremely worried, even if Emil would constantly say he was alright. He’d try finding all kind of treatments and solutions, stressing himself until he has a cure for his younger brother’s problem. He would propose different activities, thinking that if he tired Emil out well enough, he’ll fall asleep easier. If that doesn’t work, maybe some alcohol could make him pass out, even if Norge would probably kick his ass later for getting Emil drunk.
Norway|Lukas Losnedahl: Being the overly protective brother he is, Lukas would start questioning Emil all sort of things, like since when the problem started, what does he usually do. He would pester him that he should have come earlier to him and ask for help instead of trying to deal with the problem himself (and fail terribly). Lukas would try the medical treatment, searching for some pills and searching for different opinions on what other medications he should look for.
Finland|Tino Väinämöinen: Tino would feel really sorry for Emil and he’d try be as supportive as he could. He would be pretty confident on home remedies and tricks, more than other suggestions you could find on the internet. He’d prepare some warm beverage before Ice went to bed, like a glass of milk or some honey tea and would retain him from having anything sugary or caffeinated with some hours before sleep time, as it might get him hyped.
Sweden|Berwald Oxenstierna: Maybe Berwald wouldn’t show much concern, even though he was indeed worried and he had been having the feeling Emil wasn’t getting enough sleep. He would take a look from his books and try finding something that would be hard to keep focused on, especially when tired, so it could help Emil fall asleep. If that didn’t work, he was willing to borrow him some of his jazz or classic music for a better atmosphere or suggest him listening to white sounds while trying to sleep.