Hey young man you all should be gentle with your kid brother.
Your brother has a learning disability for sure. My partner has a nine year old who can't read ABC to Z? The school diagnosed and she was classed as an IEP, a student with special needs because she struggles in school. In your little man case whenever he's in a academic environment guy, the book de confuse am, the letter's or numbers de be them like say e de turn.
So advice your parents to get him into a school with individualised educational programmes. Help him to be confident again, if it's a dance class or whatever active activities please you all should involve him.
Hope you know R. Kelly suffers from that same disability, remember the grammy award he came and was to read out something he couldn't, that doesn't mean he can't read when he is calm.
Also remember everyone develops at their own pace.
My 14yr old daughter also is an IEP student, she's a smart girl but we take it easy on her but over here, but guess what in her school they gave her a personalised teacher that helps her in almost everything. In her last national Jamz Cheer competition, she helped her team came out second over other 90 school team's.
So dude don't tag that little man as a dullard anymore.

Show us the pictures of the twins in the womb, with that the staff's on duty Don loose their operating licences