What advice can you give to help my son and his children in this situation?

My son (33 years ) married 11 years ago and have two kids (boy 10 years and a girl 8 years) his wife went away with both the kids to her parent’s home about a month ago. So far she has remained very stubborn even in talking with us and not showing any interest to come back or allow the kids to start with us and my son. Although the children are at school and madrasa, and attendance to and from school/madrasa is very much stressful for kids by coming and going from her parent’s home. More over to the best of our knowledge her parent’s economic situation is very poor as they have no regular income, and due to the above two factors we are worried about our children that they continue staying with the mother. Our daughter-in-law is also not regular in her salahs, she is most of the time spending her time in watching television and chatting using her cell phone. Always angry with my son, who is now frustrated and depressed due to his wife’s attitude. This is what we have observed. Please kindly advice me.