You are about ready to have a cousin take an autosomal DNA test. Make certain that they are aware that taking this test could expose family secrets. Most people are aware that a test could reveal that they have children others have not known about or that even they did not know about.
But the DNA test could reveal more. It could reveal that a parent or grandparent is not their biological grandparent. It could also reveal that one of the testee’s relatives–including siblings, aunts, uncles, and others–either had children of which no one was aware of or whose biological parents were not who they thought they were.
It is important to remind the testee that the secrets that may be revealed may not just be about them.