[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.
Leaning back comfortably in their seats, they discussed their prospects for the time to come, and it seemed on closer examination that these weren't bad at all […] Growing quieter and communicating almost unconsciously through glances, [Mr. and Mrs. Samsa] thought that it would soon be time, too, to find her a good husband. And it was like a confirmation of their new dreams and good intentions when at the end of the ride their daughter got up first and stretched her young body. (3.38)
With Gregor's death, the Samsas appear to be a "normal" family out for a trip to the country. Mr. and Mrs. Samsa's observation that Grete is reaching a marriageable age suggests that, with Grete, a new family will emerge. Of course, given the trajectory of the entire story, one wonders if this new family will be just as dysfunctional as the Samsas.