我弟弟写作业怎么说英语

To say "my younger brother is doing his homework" in Engpsh, you can say "My younger brother is doing his homework." You can also say "My brother is doing his homework" if you want to specify that he is your younger brother. If you want to be more specific, you can say "My younger brother is working on his homework assignments" or "My younger brother is completing his homework tasks."