Many thanks geeohgeegeeoh and ExSp33db1rd for your most helpful comments and advice and also ExSp33db1rd for your explanation of the process. In some ways our ignorance of the US security process will be an advantage but like you we will no doubt fall foul of one rule or another. Family and I will be arriving on an A380 but will now plan to sit upstairs in Club as close as possible to the exit....
My only experience of US transfers was passing through Miami several times twenty or so years ago, coming up from South America before heading west. "Use the Blue priority lane sir; I've put a sticker on your passport to show you are entitled to use it". Alas on arrival the signage was in English and the majority of arrivals unsuprisingly spoke Spanish so that didn't work!