Lucifer checks up on his brothers (and you) every night after finishing his paperwork. He patrols the house at around 3am and just peeks into everyone’s rooms to make sure they’re all in bed and sleeping.
One time, he couldn’t find Asmo anywhere so he stomped around DevilDom trying to find him and dragged him back home by the collar after spotting him outside the Fall. And then he proceeded to stay awake and guard his room for several more hours to make sure he doesn’t try to sneak out again. He continued to do this for at least a week and probably still does it on occasion, simply because he worries if his siblings aren’t all at home by midnight and Asmo is too wild for his liking.
Another time, he came across Mammon sleeping on the floor of your room and carried him all the way back to his room. Then he tucked him in and came to check in on you next. He also tucked you in. You were only pretending to be asleep so you saw him do all this but decided not to say anything because he looked very happy with himself, though you were tempted to tease him the next day at breakfast.
Sometimes, he finds Belphie asleep in the planetarium. He knows better than to try and bring him upstairs since the youngest would wake up and tell him to piss off anyway because he chose to fall asleep here on the cold, hard floor and didn’t need his help, thank you very much. So, Lucifer just brings him a few of his blankets from the twins’ room and uses those to cover him up so he doesn’t freeze to death for the remainder of the night. He also does this for Satan, when he finds him sleeping in library since the fourth born practically lives there and refuses to leave even when he’s past the point of exhaustion.
Lucifer checks on Beel the most. He’s aware his brother has some pretty nasty nightmares so he stops by every hour or so to wake him up if he can tell he’s having one. He brings food too, just so that the sixth born doesn’t go raid the kitchen again. Then he leaves and never mentions it again and Beel usually can’t remember if he was hallucinating or not.
Also, after a while he catches Levi playing video games at like…4am and just turns the WiFi off so his brother can go sleep for once. The third born can cuss him out about it all he wants but he’s not budging and Levi has to admit defeat and go curl up in his bathtub. He accepted his fate and has to go along with his sleeping schedule getting forcibly fixed by Lucifer, who won’t take no for an answer.
Lucifer needs someone to tuck him in bed tbh, like he’s the only one still awake by dawn and he refuses to admit that he’s tired so he just drinks fifty cups of coffee and calls it a day and his brothers are none the wiser. That makes me sad thinking about it-