They were taking the children as the first priority as he claimed they couldn't be sure that they were carriers to the plague. Their leader Colonel Vosch explained that they had been in quarantine and now were seeking survivors. Oliver, his children and the rest of Ashpit during Vosch's Arrival

He, like the rest of the camp, was shocked when soldiers pulled up with working vehicles and buses. He became concerned when the drones started to be sighted and guessed that the Others were using them to test conditions for themselves to finally make the Earth their home. On the way there they stumbled onto Camp Ashpit and decided to stay there a while with the other gathered survivors. He felt that the base might be the safest place for them. When that was done he took his children and made to travel to Wright-Patterson.

Oliver with his children over the grave of his wife He stayed with his wife until the end and then gave her a burial in their backyard. However, it seemed that he and their children were immune to the disease. When the 3rd wave hit, Oliver's wife was infected.

With how chaotic things had become he felt that the wise choice was to hold up at home even after news reached them of the 2nd wave hitting the coastal cities. Oliver was quickly able to identify what happened as an EMP as he took Cassie home. They had to walk all the way back home through all the chaos that the EMP caused in the streets. When the 1st wave hit ten days after the Arrival, he went to Cassie's school to pick her up. At first, he debated with Cassie that the Others might be there to 'save' them. He and his wife decided to stay home and try to keep going about their lives like normal unlike a few other people around them were doing (running away, packing everything up, etc.) He explained that they didn't feel safe being in such densely populated towns but reasoned that they were as safe as anywhere for the time being. Oliver Sullivan was one of the people excited to learn about The Others when they first arrived. Oliver with his family watching the news about The Others Fifteen years from that moment, he would come to name his daughter after that constellation. The one that really had his eye was the constellation of Cassiopeia. He especially was taken by the constellations. As a boy, Oliver went on a trip to a planetarium where he lost himself at the display of stars.

Does evan die in the 5th wave