Family support

It is heartbreaking for the children, but the only people to know what goes on in a marriage is the two people involved, I don’t think you should feel guilty, you say you think they are giving up too easily, but you don’t know that they weren’t trying to make a go of their marriage, as they are more like friends , if you can part as friends that’s got to be a plus, just be there for your daughter and grandchildren

Tell them you are there for them and please ask if they need help.

Only 2 people know what happens in any marriage. Dont take sides, be available to chat things through. Much better to part as friends than stay together unhappily. And gives the children, however upset right now, a positive example in adult relationships. If they see that parting does not need to be acrimonious and damaging, they will cope and still have both parents in their lives.

Having been through this scenario just be there for them all and don’t take sides. We are 5 yrs on from my daughters breakup and they have all got on with their lives now including the 4 children.

Yes, they have made a decision so be there if they need you but let them sort it out. My family stayed in touch with my ex after we spilt in a distant way and this was good for my kids. So you will be there for your daughter but don't side with her, just in case they get back together.

How very sad all round.
Let them all know that you are there for them whenever they need you.