Jacob feared that if his other children found out about Joseph's dream, they would try to harm him in any way.
Joseph was harmed by his brothers, but not by the dream that Joseph had. His brothers did not even know about this dream. They harmed Joseph because Yaqub loved Joseph more than any other child.
The Qur'an describes it this way:
'Remember when they said,' Surely Joseph and his brother are dearer to our father than we are. ' But look, we are a whole group '. - Surah Yusuf 08
The reason behind the misery of Yusuf (as) was not his dream, but his father's deep love, compassion and great compassion for him. The other brothers began to look with envy on the father's excessive love, affection, care and affection for Joseph.