What are thoughts of testing of nieces and nephews of people you already have tested? I have two aunts tested and I've seen just what a different array of matches, and knowing the differences in cM between them is a very useful metric to narrowing down the degree of relation. I've also noted that parents and children can also have the same or similar cM with matches.
Recently a friend began tracing his tree and he's taken some tests with my advice of who to get tested. His paternal line is out of wedlock, from his grandfather. Though he was given a surname of the father and I found a newspaper article about a divorce filing between his g-grandmother on grounds of adultery with a man with that surname. Looking into the DNA matches, we've been able to triangulate four groups of matches covering each of that man's grandparents. Though each group is quite small.
His father is tested and he only had one brother, who has living children. How useful do you think it would be to get them tested?
