Hi Sara and welcome! You mentioned in your post that your brother wasn't 'book smart' and that he was unable to answer your questions and referred you to the elders. Unfortunately, this is probably why the JW's were able to get him in the first place. They look for people that may not be as 'smart' as others and people that are easily manipulated. Sad, isn't it?
The thing you do have going for you is that you are not, nor ever will be, a JW. While he will be encouraged to leave his 'worldly' family behind, he will never be forbidden to talk to you.
Is there something he may have enjoyed before joining that he doesn't do now? Maybe bring that up in a conversation and get him thinking about all the stuff he may be missing. Just a suggestion.
Good luck.
BH