while the family is waiting for papa to come in from the fieled at the day who is it that the family worries about

I think they are worried about Papa. When it is dark outside, Papa’s older stepbrothers – Tío Luis, the bank president, and Tío Marco, the mayor of Aguascalientes - arrive at the farm. Though they are family, neither Esperanza nor Mama likes Papa's stepbrothers. When Esperanza spots her Papa’s one-of-a-kind silver belt buckle in her uncle's hand, she realizes that something terrible has happened. Nobody knows where Papa is, but it is likely that bandits have attacked him.