How old are the kids? I've done exactly what you're trying to do with two 16 year-olds. (Had no problem with them on the companion certificate and not being the primary cardholder.) See here:
"Unaccompanied Minors: Alaska considers children ages 12 and under who are traveling without a parent, guardian, or other responsible Adult age 18 or older to be Unaccompanied Minors and subject to the policies described below. Children ages 13 years old through 17 years old are not subject to the policies and fees applicable to Unaccompanied Minors when traveling on Alaska unless they are connecting to another Carrier that uses different age thresholds to define Unaccompanied Minors. When two or more Unaccompanied Minors are traveling together, the most restrictive age requirement will apply."
From:
https://www.alaskaair.com/content/le...rriage/rule-13