Yeah because going after people just because they're related to terrorists by blood is a great idea.
It depends on what "going after" entails.
So you suggest that the intelligence community just ignore blood relatives or any family of terrorists just because they're related?
Logically, you should track down anyone with ties to terrorists and investigate them throughly. If anything is fishy, escalate the investigation. At the very least, they should be watched and bugged til their dying day. They have an obvious motive for possibly aiding their family in some way or at most being terrorists themselves.