This probably makes Gregor sad as he actually can understand them. The rest of the family apparently hadn't let go. They had still believed that they could fix Gregor and make him human again. That's why they took care of him and put up with something they thought was disgusting, their love for their son. The sister now says they need to get rid of him as he will ruin the family. Sounds kinda hard to Gregor but in her mind he isn't Gregor so it doesn't matter. That's very saddening.
Gregor dies and this is his dads first comment. You can tell they were a loving family. It seems that the daughter was successful in convincing the dad to let go of the idea of the beetle being Gregor because he treats his death like the largest burden has been lifted from his shoulders. He immediately kicks out the Boarders and then dismisses the charwoman. Then the whole family moves and pretends like nothing happened. The beetle died but they weren't sad that Gregor died. To me that shows they had already mourned Gregor's death and were trying to hold on by dealing with the beetle, but knew deep down that the Gregor they knew was already gone. Gregor died of a few things put together but I believe the reason he died that night was because he realized the family was going to get rid of him. They were done with him and there was nothing he could do for his family. He realized he was just giving them grief so he let