the first one might be this https://www.mangago.zone/read-manga/night_song_mgs/
Hi, number 1 seems Night Song https://www.mangago.zone/read-manga/night_song_mgs/ but number 2 doesn't seem familiar and number 3 seems missing from the comment?
Hope it helps! (●'◡'●)ノ
I think the second might be a little obscure it wasn't the most popular even at the height of its popularjty. And the third, I forgot to add!!
Basically I think it was fake relationship omegaverse manhwa
where if two people are in a relationship they get a scholarship or some other sort of financial benefit. I think it was set in uni and the mcs were dorm roommates. They had bracelets to track their heart rates to make sure they aren't scamming the school/govt by lying about being in a relationship
I know the third one is it special benefits for newlyweds?? https://www.mangago.zone/read-manga/special_benefits_for_newlyweds/
I really liked its concept, but tbh i have no idea about the second one

It's been a while since I read this so I might not be remembering details exactly but
1. It's historical yaoi manhwa where the mc was cursed as a child so he keeps seeing ghosts and can't sleep at night but he's the adopted (?) son of a lord so he tries to put up with it when a demon (?) I think one of the sons of the king of he'll gets banished from he'll cause he plays too much and the condition for his return is he has to make a human love him or something so they start sleeping with each other. The last chapter I read thr mc just left the estate and the demon was chasing him to save him
2. This is a straight love story manhwa with one of those typical "sibling comes out of nowhere and replaces the mc and their parents don't care about them anymore" type plots. I don't remember if the mc was adopted or not or if it was thr new sister. It was set in modern day, I think the mcs guy best friend left to the army then comes into the story after everything with her family falls apart. I think she was also supposed to be engaged to someone based on some promise their parents made when they were kids but because of the sister coming into their lives they asked her to drop it and just let her sister marry him. But the grandpa of the person she was supposed to marry wants her to marry the grandkid. I think the guy I mentioned from the military is his brother or friend. Help