The first pair of polar opposite siblings are oldest sisters Lori and (since someone was going through a Swedish phase at one point) Leni....or, as I like to put it, Prickly Leader and Supine Follower. I'll cover the older today and the younger next and go through the others in succession. What greets the eyes when one meets Lori is a rather pretty girl who loves to wear powder blue clothing: she's usually seen wearing a powder-blue tank top, her dressy clothes are that colour and so on and so forth: this is why she's depicted AS being powder blue in the opening sequence. At first blush, she looks like a bog-standard bossy old sister bent on making Lincoln's life a mess but there is more than that to her owing to the fact that Savino seems to have made her into the official reincarnation of Major Houlihan from MASH.
What this means is that much like Lincoln, her primary goal in life is to ride herd on her younger siblings to keep the chaos at a bare minimum. She simply sees him as being part of the chaos because for reasons that baffle her, he won't wait in line like everyone else has to; the only thing that makes him different from the others is that like her, he rolls with the punches when life offers up its steady diet of sadistic choices and downer endings. She just wishes that he wouldn't try to take over being the one doing the planning because without her authority, she feels practically undressed.
This leads us nicely to what she and Lincoln don't have in common: her need to semi-unwittingly sabotage possible competition. If someone less brusque and spikey were someone the others could go to with a problem, she would be as diminished as she is when someone makes happy talk with her emotional crutch boyfriend. This, as I'll point out tomorrow, is why her roommate sounds a lot like the punchline of a Medium Large about a kid homeschooled by an asshole older sibling who resents him.