Any ideas how or if I should try and contact her at all, or just leave it up to her.
Can you just try family emails for awhile? Sounds like staying in touch with the children is important to you. I know you want to find out how they really are from your wife's perspective, but that doesn't seem to be working from what you said. I haven't read all your old posts so I am not clear on your relationship with your children. You said they are sad. Sad because you are gone? Sad because their sister is away? Sad that their parents are not together?
My D16 acts they she doesn't care if her dad and I divorce. But I know she does by the questions she asks. I think the unknown is hard for her, but doesn't want to show her feelings.