You can translate this in an active form. Alternate translation: "that he would change them to be like his Son" (See: [[rc://en/ta/man/jit/figs-activepassive]])
Here "brothers" refers to all believers, both male and female. Alternate translation: "among many brothers and sisters who belong to the family of God" (See: [[rc://en/ta/man/jit/figs-explicit]])