150 kids from one sperm donor

Accidental incest is a concern.  (International Business Times).
A 48-year old woman who gave birth to a son through artificial insemination was shocked to learn that he has 149 siblings, with more on the way, the New York Times reported. Cynthia Daily used a Web-based search to connect with other families who had used her sperm donor, with the thought her son might be able to connect with a few siblings one day. But she could not have imagined the extended family would amount to the size of a typical high school graduating class in the U.S.

‘It’s wild when we see them all together — they all look alike,’ said Ms. Daily, 48, a social worker in the Washington area who sometimes vacations with other families in her son’s group.” (Quoted in Instapundit).
"My Son's Group" - is that like visiting the cousins?