Why do Mr. Samsa and Grete refuse to follow Mrs. Samsa to clean Gregor's room?

I see no refernce in the text to either Mr. Samsa or Grete refusing to follow Mrs. Samsa into Gregor's room while she cleaned. Cleaning Gregor's room was Grete's task, and the one time her mother cleaned the room, Grete became very upset. Does this question pertain to a specific chapter?

"Gregor's mother did once thoroughly clean his room, and needed to use several bucketfuls of water to do it - although that much dampness also made Gregor ill and he lay flat on the couch, bitter and immobile. But his mother was to be punished still more for what she had done, as hardly had his sister arrived home in the evening than she noticed the change in Gregor's room and, highly aggrieved, ran back into the living room where, despite her mothers raised and imploring hands, she broke into convulsive tears."