Morning!
A couple of things:
This is the point at which clearing lists will start to become more accurate - i.e. reflecting what's actually happened over the past few days, rather than predictions of what might happen. So if DCs have been looking at clearing lists over the past couple of days, they may be advised to go back to just double check nothing's changed (in my experience it's more likely that courses will have been added than taken out, but that's only my experience....)
Clearing lists will publish required grades for each course. There's no one rule as to how seriously to take those - although I would say that if a course that normally needs As and Bs has dropped the requirement in clearing, that may be an indication than they really need to fill places. The reverse may not be true, however - if they haven't dropped the requirement they may still unofficially take the odd person on a grade below (or they may not) - it's worth ringing to ask. But if you ring and are told no, take that no and move on - when you ring you will most likely initially get through to a call centre with people who are working to instructions and they will have been told who to forward on and who to turn down.
If you are thinking of clearing, get the applicant to do some thinking about what they are going to say. At some point in the process they may (or may not) be asked to explain why "subject" or why "university". They don't need to launch into this straight away to the poor benighted call centre operative, but if they are asked they need a coherent answer. It's also a good exercise to help them think about what they really want, and whether a clearing place is a good thing.
Many universities with clearing places will offer an opportunity to visit over the next few days. If you haven't visited before, your DC should, if at all possible, take that opportunity. Clearing applicants are substantially more likely to change their mind and pull out of a course early.
I'm afraid there is no way that today isn't going to be stressful and horrible. This too will pass, however. One thing worth saying (and I say it with caution, because it is not for me to tell you how to parent your DCs!) is that anxious young people are surprisingly often anxious because of a fear of letting their parents down (and often reluctant to talk to their parents about that fear - they talk to others about it.). You are all stressed because you want your children to get what they want. Even if they are grumpy and teenagerish about it, I bet you it will help them just to know that fact, and to know that, whatever grades they get and whatever they end up doing, you are still proud of them.