Thanks to the people that replied. I still haven't gotten around to sending any of this stuff to older brother... first I should probably get together with him socially (without my fiance) and bring the conversation around to it, so I can feel out how receptive he is. I got one useful reply via PM from someone who wants to be anonymous:

There are two people on this site who are very familiar with PUA stuff and not enormous gits. Wedrifid is not a self identified feminist but see this

http://lesswrong.com/lw/68m/discussion_socially_awkward_penguin_as_a_tool_for/4ddk?context=1#4ddk

For some indication that he has a relatively nuanced grasp on social interactions see here

http://lesswrong.com/lw/68m/discussion_socially_awkward_penguin_as_a_tool_for/4dr7

For LW's resident feminist PUA his collected works can be found here

http://lesswrong.com/lw/44r/post_proposal_attraction_and_seduction_for/43aj?context=1#43aj

No doubt he has some kind of email address on feministcritics.org too.

I would ask both of them for advice. More viewpoints are better. I suspect you can't give your older brother advice in a way that won't make him feel bad.

Speaking from my own experience (as the brother who was obviously less successful than the younger brothers) if he's in a bad enough situation the blow to his pride will be ignored in favour of inspecting the possibly useful advice.

I believe the PUA known as Juggler would be acceptable, as generally not a hideous misogynist. I know that the founder of the modern PUA subculture Mystery has changed the vocabulary in his guide, e.g. from "bitch shield" to "protection shield". He's probably not actively poisonous, torrent "Mystery Method"

If you can't get anything else out of this the easiest things that are completely socially acceptable to say to your brother are

Exercise. You will feel better and look better. For maximum benefits for time spent lift weights, squats, benches and deadlifts. If you don't have gym access, squats and press ups. NO SIT UPS. they fuck up your back,

Get a decent haircut. Note, this can include having your hair so short it's not there, or so short it stands up. It must not look crap.

Learn to distinguish "This fits me" from "This doesn't" when it comes to clothes. If he can do that and is willing to throw out all clothes that don't fit he's doing better than 50% of men. At least. For advanced classes he could go to reddit.com/r/MaleFashionAdvice

Being a cool, interesting guy who's having a good time is attractive.

Being needy is not attractive.

I'm done. Hope this helps a little.