Don't know what to do

You and your friends have both only heard one side. I would not say anything as they will support their son and you will lose your friends.

I would be a listening ear but not get involved as you say she has friends and family in the UK that she can contact.

I really wouldn't mention anything to your friends unless they talk to you about it and even then it may not be a good idea to let them know you know so much about the situation. It's lovely you're supporting the DiL but it's a bit like treading on eggshells as your friends may feel this is taking sides if they find out. Be sympathetic by all means but don't be critical of the son - after all you've known him all his life and whatever has happened between the two of them you are only hearing one side of it.

Not a good position to be in.

Apologies in advance if I haven't understood your post correctly, but I agree that when you meet your friends you should not comment at all on the situation unless they introduce the subject.

As regards your d.i.l, if she cannot work because it is her husband whose visa permits this, would it not be better to return to the UK?

Not questioning anything you say, but isn’t it mostly true that there are two sides to any story?
While you may be able to express your regret at the breakup of the relationship, this can’t be before they mention it and you are certainly not in a position to criticise their son.
Only they may do that as most of us would close ranks and defend our offspring even to close friends.
If their friendship matters to you, keep any criticism to yourselves.
See how the land lies, there may well be a way back from this and to be too outspoken would be likely to be curtains for your friendship.

Smileless, you must stand up for the righteous ......your friends' son seems to be unreasonable.
You must continue to support the young woman, and I also think his parents should be aware of the situation. It's going to be awkward for you and Mr S when you meet them next week. I, personally would not be able to keep it from them, but then I tend to talk too much. I'm hopeless at keeping secrets.
Isn't it awful when marriages end? It's a good thing there are no children involved.
Good luck Smileless !

Try to say nothing , if you take sides it will not go well if things calm down and you really can't help the poor woman . If you fall out with your friends it won't help either

I have no idea but didn't want you to think there was no one else out here on the forums. Its hard as really its no one else's problem and there is the issue of confidentiality. I
suppose if they mention it when you meet then you will have to be led by their conversation. Not easy for you .........