What do the Samsas' three boarders represent in the Metamorphosis?

The three boarders move into the Samsas' house so that the family can make more money after Gregor, who has turned into a bug, can no longer work. The roomers are very tidy people, and they "were painfully insistent on things' being tidy" (page 35). They bring a lot of their own furnishings and belongings with them, which means that the family's belongings have to be crowded into Gregor's room. Eventually, even the dustbins from the kitchen are relocated to Gregor's room. The roomers spot Gregor one day, and they threaten to move out. The next day, after Gregor dies, Mr. Samsa finally has the courage to throw the roomers out of his house. 
The roomers represent the intolerant attitudes of the outside world towards Gregor and the travails of the family. The roomers do not belong in the family, but they unthinkingly take over the apartment and make harsh demands on the family. They push Gregor towards death, as they make him realize that he is a burden on his family. The roomers' intolerance and narrow-mindedness are what finally kill Gregor. After his death, his father realizes that the roomers and their intolerance have to go.