As they continued onward, they encountered many outposts under siege. Sometimes, it was difficult to tell who the invaders and the defenders were. When it came to those times, they pressed onward, trying to stay out of it. If they were attacked, John would defend with a gravitational barrier like before. If that wasn't enough, they had Rose and Jake help keep the heat off of them, even if it meant killing.
As for the times they did help? Well, it was only when it looked like the defenders really needed it. Rebecca and Henry took Vermillion's opinion seriously, so if they felt like their time was being wasted, they didn't stop to help. It may have seemed cruel, but if an outpost was close to being defeated or was flawlessly winning, there was no point in trying to help.
Why?