How we cite our quotes: (Chapter. Paragraph)
Quote #1
He applied himself to that pastime with great industry, with his elbows spread out and bowed low over the kitchen table. Through the open door of the parlour at the back of the shop Winnie, his sister, glanced at him from time to time with maternal vigilance. (1.15)
This is the first real taste you get of the devotion that Winnie has for her brother. The mention of the word "maternal" shows you that Winnie acts more like a mother to Stevie than a sister. Your sense of this devotion will only get stronger as the story unfolds, but at this early moment, you're just given a hint of it. Winnie watches Stevie as he draws his circles, a perfectly innocent activity that makes Stevie seem kind of childlike. Check out Conrad's wording, though, which doesn't say, "love," but "vigilance." Winnie's devotion to Stevie is not the same thing as compassion. It's protective, stubborn, and maybe a little competitive.
Quote #2
There had been a steady young fellow, only son of a butcher in the next street […] with whom Winnie had been walking out with obvious gusto […] [Then] that romance came to an abrupt end, and Winnie went about looking very dull. But Mr Verloc, turning up providentially to occupy the first-floor front bedroom, there had been no more question of the young butcher. (2.138)
Winnie's sacrifice seems to be a bit lost on her mother, who thinks that the end of Winnie's relationship with the butcher boy was something "providential" or god-sent. The woman turns a blind eye to the fact that Winnie has given up her true love for the sake of her family. Who knows? She probably knows the truth deep down, but feels guilty about it. With this decision, Winnie no longer lives for herself, but lives only for the safety of her brother. It's not really clear if the novel supports her decision, because her sacrifice only leads to death. Who knows? Maybe she would've had a chance at a good life if she'd married the young butcher boy, and maybe Stevie would've been able to survive. At the very least, they would've had first dibs on all the prime rib they wanted.
Quote #3
Mrs. Verloc, turning towards her recumbent husband, raised herself on her elbow, and hung over him in her anxiety that he should believe Stevie to be a useful member of the family. That ardour of protecting compassion exalted morbidly in her childhood by the misery of another child tinged her sallow cheeks with a faint dusky blush. (3.74)
Here, the narrator actually uses the word "compassion" to describe Winnie's bond with Stevie. It suggests that this bond was created in their childhood, when Winnie had to protect Stevie from their abusive jerk of a father. We see here that Winnie's bond with Stevie seems to come directly from their experience of abuse, and she's come to think of Stevie as an extension of herself. He represents total innocence and helplessness to her, and this is probably why she's able to sympathize directly with the pain he's felt, because she's felt it, too.