I haven't read the full thread but sorry to read that some of your teens are still a bit up in the air after an Oxbridge rejection.
A few years ago, DS was in a similar mindset. He was feeling a bit 'meh' about his other offers - LSE and UCL have great reputations but he wanted to get out of London. Durham, as mondaytosunday says, has this reputation of 'posh' and 'Oxbridge-lite.' I think this is really unfair actually, because it's not as if there aren't just as many so-called 'Oxbridge rejects' at other top unis. Bath had made him an offer but it was something like AAB and I think he just felt there was no point in working hard for all A stars and then taking that offer.
So he did reapply and was successful second time round. He also knew about 5 others who reapplied and were also successful and, once in the uni, realised loads had had gap years and / or reapplied. It's actually very common indeed.
My only advice would be - don't reapply with the same application! It's important to do something relevant to the degree in the gap year - they will want to know what you're doing and why. And really, given how competitive it is these days, it's only really worth applying if they have very high / perfect grades. Also, anything they can do to boost their application like essay competitions, articles for magazines, activism, online courses - anything. They will expect more from a post- AL applicant than one who is still halfway through A-levels. If possible (it's not for all subjects), go for a college that has a 'general interview' as well as an academic interview, because then they can talk about their voluntary work (or paid), extra essays or research pieces they might have done etc etc.
To be honest, by the time August comes, January doesn't seem far off. And it's an unconditional place then, if successful.
Secind time around you could also broaden the search -eg. look at options abroad, so that it's not all about Oxbridge. And make the gap year worth it in itself, whatever the outcome. Have a clear plan would be my advice because it can be hard for them when all their friends are posting about uni in social media.
Having said this, everyone we know who has gone to Edinburgh, Durham, Bath, St Andrews etc absolutely loves it. Once they are there, they never look back and their lives take off. I think LSE and Imperial are different uni experiences, especially for those who live in London anyway. But, let's face it, one is in South Kensington, one just off Covent Garden. There are far far worse places to be a student! They are very lucky indeed and they will make friends wherever and what will be will be.
Best of luck to them for any outstanding offers. Hope this is not too waffling.