Your brother might want to go for testing, as it is genetic. It's a simple blood test. they give you shot, and then 4 hrs later take a blood sample. It's not 100% conclusive, but still quite effective. Also, you don't mention the ethnic background of your sister-in-law. There is a higher rate of carriers in people of Northern European descent than other areas. (eg. Asian descent has virtually no carriers. Germanic has high) Something else to throw into the equation. Tom