Yes, every family member for which the I-485 application has been approved must show up in person for the PP stamping. If they can write their "signature" (first and last name) in the tiny space on the I-89 form they must do so and give a fingerprint - the officer can waive the signature and fingerprint requirement for young children.
In my case, the 3rd-grader and 2nd-grader had to sign, while the Kindergartener got a waiver and thereby got upset for not getting to give the fingerprint like the others had. Kids...
