It should also accept "I really miss my older brother". Same meaning.

Not wrong grammatically or in meaning, but it doesn't seem to me that people would say 非常+想...

很想、真的很想 are more usual.

This is such an emotional lesson.

I miss my older brother a lot. I wish he was here to punch Duo in the beak.

why "I miss my older brother very much, I want to cry." is not accepted?

I miss my older brother so much, I would like to cry. Guysss, why don't it makes sense. :(