How we cite our quotes:
It was always arranged, when possible, that [Gwendolen] should have a small bed in her mamma's room; for Mrs. Davilow's motherly tenderness clung chiefly to her eldest girl, who had been born in a happier time. (3.9)
Gwendolen's family dynamic is an interesting one. Even though Gwendolen can be rude and hateful, her mother still gives her the most devotion because she reminds her of a better time of her life. Isn't it interesting that we actually don't really know anything about her sisters, even though they're around all the time? They just sort of float around in the background.
Mr. Middleton was persuaded to play various grave parts, Gwendolen having flattered him on his enviable immobility of countenance; and at first a little pained and jealous at her comradeship with Rex, he presently drew encouragement from the thought that this sort of cousinly familiarity excluded any serious passion. (6.24)
As far as Mr. Middleton is concerned, there's no way that there's anything romantic going on between Gwendolen and Rex because they're cousins. We think Rex would beg to differ.
No one was better aware than [Sir Hugo] that Daniel was generally suspected to be his own son. But he was pleased with that suspicion; and his imagination had never once been troubled with the way in which the boy himself might be affected, either then or in the future, by the enigmatic aspect of his circumstances. (16.44)
We get a whole lot of information in this quote. Sir Hugo is happy that people think that Daniel is his son, but this gives us, the readers, the hint that Daniel is not Sir Hugo's son. This moment also reminds us that Sir Hugo doesn't have any sons in the first place, and that's why Grandcourt gets to just show up and assume that he'll inherit all of Sir Hugo's property someday.