Both stories concern human relationships after a change has occurred. In Kafka's short story "The Metamorphosis" the family must think about dealing with Samsa who has turned into a "gigantic insect." Greta is perhaps the only selfless one. But the rest of the family seems quite selfish in the fact that they worry over the loss of their major breadwinner rather than showing true concern about Samsa's welfare.
We see a somewhat similar reaction in Hemingway's short story "Hills Like White Elephants." The girl in the story is pregnant. The relationship she has with the man has therefore come to a crossroads. The man, like Samsa's family, would like to maintain the status quo. He wants things to be the way they always were. He wants the girl to have an abortion.
A good focus in comparing these stories is how the other characters react to the "the metaphormosis" of the main characters. We learn much about the values, personalities, morality of the other characters in their responses.
I hope this helps.