Finding relatives

I’M ANXIOUS to contact the family of my cousins of whom nine haven’t had contact for something like 50-60 years. 
David and Matt Williams are the children of my father’s brother James Williams who moved from Ynysybwl to a Caerwent smallholding presumably in the late 1920s/30s during the depression. 
James was one of three boys (Hugh, James, Robert) and two girls (Margaret – Peggy and Betty) the children of Robert and Margaret Williams of Other Street, Ynysybwl.
There was also a younger sister to David and May namely Glynis who died a young women.
It would be lovely to meet these relatives after all these years.