OP, in the nicest possible way, I think you all need to give your head a wobble.
Firstly, your younger DD is only in Year 10 and predicted grades are not even accurate.
Your elder daughter chose not to apply to Oxbridge so, it is what it is. Why all the recriminations now?
My son is in a school that achieves about 90-95% grades 7-9 at GCSE every year. Has he at times struggled with feeling very average at best? Yes he has.
But you know what, if the competition doesn’t hit them at school, it sure will In later life. At least they’re less likely to be phased by a competitive job application process, for instance, or job rejections. Resilience is part of education. I’ve often had to have the talk with my son that “comparison is the thief of joy,” etc etc and nobody else’s grades matter. But actually, the truth is, that I do credit DS’ friends with his GCSE results - more than the teachers
This is because he was so worried about being the only one to get 6s, that he ended up achieving 10 grade 9s and he couldn’t believe it. More than anything, it’s been a useful lesson in life, that hard work pays off in the end.
So now he has friends going on and in about Harvard applications etc (which is a whole other ballpark)! and sometimes it does get on his nerves. He can get overwhelmed at times. But he knows he’s fortunate to have the education he’s having and there’s no point blaming the school. If he gets the predicted grades after Easter, he’ll have a shot at Oxbridge, but he’s not comparing himself to other friends who are applying because nobody else is applying for his subject so it’s irrelevant. He’ll choose 5 unis and there will be pros and cons to all of them. Cambridge doesn’t offer a year abroad, while the others do. You can’t tag on a language at Cambridge, while you can elsewhere. This is the way we’re going into it and wherever he ends up will be right for him. I keep telling him that my coming to London to study was a complete fluke, but this was where I met his dad, so maybe it was meant to be 
Your DD has great offers and once she’s there she won’t look back, I’m sure. Go and visit them again maybe?
My son gets wound up but he also gets a reality check because his school get them doing community work as part of the A-level programme, so he’s doing tutoring to kids who will be lucky if they get 4s/5s at GCSE. This is the national average and they’ll be fine too. Maybe show your daughter some national data? She’s doing really well and has nothing to worry about.