My comment:
(a) The report is locked behind WSJ paywall.
(b) "Sonny and Brina Hurwitz raised a family in Boston." On the surface, the couple (now deceased) had two daughters and two sons.
One can click at the photo to enlarge it. It appears to me that children of black-white couples vary greatly in skin colors and appearances.
(d) "Siblings share around half their DNA. Half-siblings share a quarter, and first cousins, on average, share 12.5%."
(i) The key is "around." A human has 23 pairs of chromosomes (22 autosomal and one sex).
(ii) In theory, a parent must share about 50% of DNA with his or her biological children -- "about" taking sex chromosome into consideration.
(iii) Theoretically a father can one in each pair of autosomal chromosome to one son and the other of the same pair to another son (a father has to give hand down X chromosome to a daughter and Y chromosome to a son); hence two brothers of the same parents in theory shares DNA from 4.3% (ie, 1/ 23) to 100% -- each figure with its own probability (it will be a normal distribution peaking at 50%). Brother and sister of the same parents share DNA 0% to 95.7% (22 /23). Therefore in organ donation, a sibling may (or may not) be a better match than his/her parent or child.
(iv) Thus when one encounters related DNA in the search, to ascertain relationship between the two, one has to construct a family tree (until the two share the same ancestor). That is criminologists have been doing.