What a difficult situation for you. I would certainly try to contact your son. Although it may not be easy, tell him you love him and want him, his wife and your GC to be safe and have a good future whether they're together or apart. Without more information, it will be hard for you to know whether he has planned this to be with another woman or is really struggling with his mental health (even considering they may be better off without him and contemplating suicide). If he won't talk to you, is there another relative, friend or colleague he would talk to? Absolutely give your DiL and GS as much emotional support and reassurance as you can. I don't think making an offer of taking on long-term financial responsibility for them is the way forward but, if you're able to, then short-term help with essentials or money for travel back to UK might be the right thing to do. You don't say whether DiL has other family in UK or where they are now. As others have said, you need to look after yourself too. I hope things get resolved and that your GS in particular knows he is loved and has a secure future in all of this.