The man with 400 children

Newsweek tells the story of a sperm donor:

[Kirk] Maxey, 51, happens to be one of the most prolific sperm donors in the country. Between 1980 and 1994, he donated at a Michigan clinic twice a week. He’s looked at the records of his donations, multiplied by the number of individual vials each donation produced, and estimated the success of each vial resulting in a pregnancy. By his own calculations, he concluded that he is the biological father of nearly 400 children, spread across the state and possibly the country.

At the time, there was little screening for disease or genetic issues, so now Mr. Maxey is crusading for better regulation of the industry. He is worried, among other things, that some of his progeny might meet each other and have children of their own, even though they are brother and sister. Recently, two of his offspring–his daughters–traced him down as their real father. Now they get together sometimes. Here they are, going out for ice cream:

Sperm donor & two of his offspring

List the different ways this is wrong.

HT: Kirk Andersen