Just to add to the strong points of the above response:
Addie is so perverse in her hatred of Anse that she dislikes all of her children but the "love child" that she has had with the minister, whom she has ironically named Jewel.
Anse is degenerate both in body--hunchbacked with gnarled hands--and soul. In essence, he is sociopathic. He uses his children, forcing Jewel to give him the beloved horse so that he can obtain more mules to pull the death-wagon after the others drown, he scrimps on money, depriving the family of necessities. Even his promise to his dying wife has a self-serving motive behind it: to buy a set of false teeth for himself.
Darl is profoundly jealous of his brother Jewel that he tries to separate Jewel from his mother while she is dying by volunteering him to go with him to obtain lumber for her coffin. So intent is he upon not allowing the coffin to make its destination in order to foil his mother's dying wish that he sets the coffin and the barn it is in on fire. As he is on the train to be committed to an asylum, Darl laughs and talks about himself in third person.
Cash, as already stated, is preoccupied with his tools. But, he is so obsessed that he views his family members as a tool. (How dysfunctional!) He actually names each member of his family with a tool.
Dewey Dell is so ingenuous and crass that she believes that a white powder will cause the abortion she desires. When a pharmist tells her to come back in the evening and he will fix her problem by having intercourse with her as this act will reverse her other act, she believes him. Later, she realizes that she has been tricked. She pushes for Darl to be committed because she fears that he will reveal her pregnancy to the other family members.
Vardamann is the youngest; he does not understand his mother's death. But, on the journey, Vardamann grows closer to his brother Darl and feels the loss as Darl is shipped off to the sanitarium. Because Vardamann struggles to understand Darl's insanity, he becomes more humane than the others of the family other than Jewel, who does truly love his mother.
As also stated by mstultz72, the family is wounded spiritually and physically after this dysfunctional odyssey of theirs. Indeed, this is much in contrast to normal funerals which usually unite members of families.