How we cite our quotes:
[T]he apple remained imbedded in his flesh […] reminded even his father that Gregor was a member of the family, in spite of his present pathetic and repulsive shape, who could not be treated as an enemy […] on the contrary, it was the commandment of family duty to swallow their disgust and endure him, endure him and nothing more. (3.1)
It's utterly ridiculous that a mere apple could serve as a reminder to the family of their family obligations, but there you have it. The story seems to be saying that family duty is a good thing, which it is insofar as it keeps the other family members from assaulting Gregor. But then the story says that family duty doesn't involve love or affection, but merely the obligation to "endure him and nothing more." The story seems to be saying that family duty basically boils down to suffering the company of people you got stuck with because you happened to be born into their group. Ouch.
"I won't pronounce the name of my brother in front of this monster, and so all I say is: we have to try to get rid of it. We've done everything humanly possible to take care of it and to put up with it" (3.17)
By the time we get to this quote, the apple in Gregor's back is now covered with all kinds of trash (see Quote #7 above). Maybe Grete can forget her family duty so easily here because she can't see the apple anymore? In any case, she refuses to acknowledge the bug as her brother and calls it a "monster." The ease with which Grete can forget her family duty contributes to the story's generally scathing attitude toward family obligations.
"It will be the death of you two, I can see it coming." (3.20)
Grete continues to insist that Gregor is no longer part of the family. In fact, according to her, Gregor is contributing to the disintegration of the family and must be eliminated.