What is the reason that all the holy tribes (except for Benjamin) went to Egypt for food? Couldn't they send only several of them or to split themselves and go in different time? Or even send some of their people to Egypt instead of them? The question is applicable even for the reason that they went for searching Joseph, they could use the same strategies mentioned before. If they would have used the strategies mentioned before, they wouldn't risked themselves?
The Ohr Hachaim הקדוש gives 2 answers for this question:
עשרה. אולי הלכו כולן לחשש הרגיל בשני רעב כי תרע עין אדם ברעהו ועל פת לחם יפשעו לגזול ולהרוג איש אחיהו, לזה הלכו כולם כדי שאיש את אחיהו יעזורו, וגם בנימין היו רוצים להוליכו עמם אלא שיעקב לא רצה, והוא אומרו ואת בנימין לא שלח וגו', הא למדת שזולת טעם זה גם אותו היה שולח עמהם:
עשרה, ten. During famine, more than during any other time, people are extremely miserly and malevolent; they are apt to commit robbery and even murder to secure a piece of bread. This is why all the brothers went down to Egypt. If attacked, they could help one another. They also wanted to take Benjamin with them, but their father demurred. This is why the Torah makes a point of saying: "he did not send Benjamin." Had it not been for Jacob's concern that an accident would befall Benjamin he would have sent him along.
עוד נראה שלא היה מוכר יוסף אלא דבר קצוב לכל אחד, ונתחכם בזה לב' דברים, א' נגלה וא' נסתר, הנגלה כדי שלא יתתגר אדם בתבואה, ויש בזה שבח לו ושבח לקונים, שבח לו כדי שישתכר הוא בכל עליית השערים, ושבח לקונים כי הוא לא יעלה השער ביותר, ואחד נסתר כדי שיבואו כל האחים אצלו כמו שכן היה כי באו כולן לקנות כל אחד הקצוב:
Besides, it appears that Joseph was selling a fixed amount of grain to each purchaser. He had two objectives in mind, an obvious one and a secret one. The obvious objective was to prevent speculating in grain if someone were to purchase an amount larger than for his own needs. Joseph's method was of benefit both to him and to the purchasers. By refusing to sell large quantities at one time, Joseph could take advantage of any rise in price when it occurred. The customers benefited by what he did since Joseph did not raise prices unreasonably. Joseph's secret objective was to force each of the brothers to make a trip to Egypt to provision himself as he only sold rations for one family at a time.