A/N: This is a request from @Kai-The-Saturn. I changed it to just a sibling(s) since some of you might be the oldest and not have any older siblings. If you have no siblings, just pretend you do. Enjoy!
Lucifer: Was polite and respectful. Your sibling(s) was very fond of them. Your sibling(s) was very happy that you chose him. However, he/she was very confused about his name since it's the name of a demon. You and Lucifer awkwardly chuckled. Your sibling(s) didn't know Lucifer was a demon.
Mammon: Was very nervous and wanted your sibling(s) to like them. He actually decided to take you all out for lunch to get to know your sibling(s) better. He actually paid for the meal and took you and your sibling(s) out shopping. You were surprised about how generous he was being. Your sibling(s) seemed to like him. However, Mammon was sulking when he got back since he spent so much money.
Levi: Was super awkward. Your sibling(s) was confused about the way he was acting. You and Levi had to leave early since he was having a minor panic attack. Once he calmed down, he apologized to you about the way he was acting. You said it was fine but was secretly happy that he didn't go into too much detail about anime when he was there. You're fine it it but wasn't sure if your sibling(s) would be fine with it.
Satan: Similar to Lucifer, he was very polite. He fascinated your sibling(s) with his knowledge and recommended them some books he enjoys. In turn, your sibling(s) did the same. They were confused about his name. Satan told them not to question it and took you back home.
Asmo: Was overly flirtatious with your sibling(s). He was constantly hanging on them and trying to charm them. However, you warned your sibling(s) in advance about looking into Asmo's eyes. You scolded him for what he did and your sibling(s) felt very uncomfortable uncomfortable around him.
Beel: Your sibling(s) was very intimidated around Beel since he was so big and strong. However, they soon came to love him since he was just a big teddy bear. They were also impressed with his huge appetite.
Belphie: Would be very gentle with your sibling(s). He would make sure not to fall asleep mid-conversation. Your sibling(s) seem to like him. However, Belphie passed out the moment you returned home since he was so tired.
Diavolo: OMG, your sibling(s) loved him! He bought them gifts and was extremely polite. Your sibling(s) saw how happy you were with him and felt he was the right choice for you.
Barbatos: Your sibling(s) felt like they've been pampered after meeting him. He went full on butler when meeting your sibling(s). Your sibling(s) wanted him to relax but he didn't listen. They started calling him a housewife after that.
Simeon: He invited you all to the cafe to chat. Your sibling(s) was awestruck by how perfect Simeon was. " This man is the spitting image of an angel." They said. You and Simeon had to hold in your laughter.
Luke: Your sibling(s) loved him. Luke baked them sweets so they could get along. They loved the sweets and his cuteness. Later on they told you he reminded them of a Chihuahua.
Solomon: Your sibling(s) were a little skeptical of him since he was so mysterious. But they enjoyed his company nonetheless. However, unbeknownst to you, Solomon ended up cooking dinner for you and your sibling(s). Your sibling(s) thought Solomon was trying to poison them and vowed to never eat his food again.
Mephistopheles: Your sibling(s) adored him and he adored them. He knows what its like having a sibling so he wanted to treat yours like his.
Raphael: Your sibling(s) were very scared of him. The entire time he was quiet and kept glaring at them. He was also acting really possessive of you.
Thirteen: She acted a little rude towards your sibling(s). She also tried asserting superiority over them at one point. You get that she doesn't have a good relationship with her sister but that doesn't mean she gets to ruin the relationship you have between your sibling(s). You scolded her when you two returned home for the way she acted.