Hello everyone!! So I've had this story in my head that is sort of a spin on the zombie apocalypse theme. The spin is that there is an alien species that's made it's way to earth, and this alien species requires a host in order to survive and it finds us humans. It essentially eats out our brains and takes the body over. The hosts will then mutate into crazy creatures who want to eat humans, and other fellow aliens. Thus mayhem and destruction ensues and we now have our apocalypse. Now here's where it gets very sci-fi. The story takes place in the distant future. Where us humans have found another planet that is very similar to earth, however, we don't know if it's inhabitable for life. Fast forward to when the aliens show up and humanity is given no other choice but to take to the skies and escape to this distant planet in the hopes that humanity will continue to exist and prosper. So many many ships are taking as much people as it can in a hurry as the human race is quickly being eradicated by these aliens. Along with people they take weapons, medicine, and resources necessary to sustain human life. Now to the question, the story follows this young family of 3 (mother, father, daughter) as they struggle to get the very last helicopter that's picking people up to take to the spaceship. This is the beginning of the story and is a short chunk of the story. They all make it to the helicopter, however there is a problem. The helicopter can only fit two more people. The father makes the decision to stay behind so his family can survive. Before the helicopter leaves, he says his goodbyes and promises his family that he will one day find them and be reunited so the can live happily together. Now we have our first protagonist, the father. Fast forward 20 years later and the human race had succeeded in making this planet their new home, while Earth had been taken over by the aliens. The father had managed to survive all this time and continues to search for a way to reach his family in any way. While on the other side, the human race has made a special team of highly trained soldiers who fly back to earth once and a while to gather resources that have been left behind, and to study these aliens. All human life on earth is thought to be non-existent, but not to Susanne Karmile, the Father's daughter, whose joined this special team of soldiers in the hopes that her dad kept his promise. She plans to find him one day on one of her trips back to earth. Susie has a mission to go back to earth to gather resources as always. She and her squad suit up and arm themselves. On the way down to Earth her ship malfunctions and crash lands on Earth's crummy surface. Susie and her squad now must survive on Earth until they can repair their ship in order to go back to their new home. Susie is our second protagonist. Now what I need help on is I don't know which one to focus on. The father or Susie. They're both survival stories although both have VERY different things that happen to them. Susie Is a trained soldier, and her dad is a self trained hunter/ survivor. Susie has a squad and her dad is alone. Two very different dynamics going on. I don't know which one should be more focused on or If both should just be equal and the story just alternates between the two. OR if there should even be two protagonists! So I ask you guys, how should I approach making a story like this with two protagonists and do you have any tips I can use, maybe from experience?