Instinct and Nine are confronted by the same questions about the barrier, and it turns out Instinct is out of luck. As long as the barrier is up, he won’t be joining the fight.
Nine on the other hand has no problem. I’d been wondering about that week if you recall. She’s an android, not a person. She’s an inanimate object with no soul, so the barrier can’t distinguish her from a trash can. She can walk right through, and that’s what she intends to do.