Sleep: This is a big problem at our house. A big issue.
D17 is a night owl who is basically unable to fall asleep before midnightish but has painfully early (zeroth hour, literally!) classes; she gets 5 or on a good night 6 (on a bad night, 3 or 4) hours of sleep weekdays, between 9 and 11 weekends. Her doctor recently put her on early-morning light therapy to see if that lets her fall asleep earlier, but it’s too early to tell—but she’ll still only be getting 6 or 7 hours of sleep given her homework load.
D19 also has zeroth hour classes (hello to her fellow bandmates!), but can fall asleep whenever she wants to; she usually keeps herself awake late enough that she only gets 6 or 7 hours, but if we’re actively on her about it she’ll get 8 or 9. Weekends she usually gets 9 or so.
D23 has a lot of trouble falling asleep—not as bad as D17, but still pretty bad. She and her younger sister don’t have to get up quite as early, but we all have to get in the car at the same time (since we remain stubbornly a one-car family), and some mornings she has classes that start as early as her older sisters (more band!), so she gets between 9 and, after bad nights, 7 hours per night, with weekends generally being 9 hours.
D25 generally gets 8 or 9 hours of sleep a night. She’d the most morning-person of our whole family by far (which doesn’t actually make her all that much of a morning person, really, but still), and so she still tends to get up early enough on weekends that she’s getting 9 hours.
Sibling rivalries: D23 and D25 are already shaping up for a war for the ages. There may be hope, though, since D17 and D19 used to fight a lot (not helped by how competitive D19 is—our whole family’s competitive, but I believe hers is a few too many standard deviations away from the average once in a while), but now that they’ve branched off in different directions (D17 more of your standard educational path, D19 into design) things have cooled down a lot. (D19 also now appreciates the D17 is the dutiful daughter, and so takes a lot of the pressure off D19 to do household chores—I do think she’s dreading her older sister going off to college and leaving her with the responsibility of being the oldest.)
On the flip side, D23 utterly adores D19 and would defend her to the death, and D25 and D17 have an absolutely delightful relationship (though not to the point that D25 isn’t excited about the possibility of taking over D17’s room to get away from D23 next year, of course).