The trailer of the movie is the most interesting and that's the only best part. It starts good introducing the characters and then the apocalypse starts from there the graph goes downwards, the sister character is unnecessarily chaotic, the brother has no character depth his presence doesn't matter much and the character of the mother has depth and also a slight character arc.
At first the storyline goes simple and understandable but it goes over the top towards the end where the character makes a forceful bad turn the reason for which was never shown, then (* Spoiler Alert) they decide to kill the sister by the doctor - I mean if she is the cure why would a doctor kill her, after that with the defibrillator they used it with the brother but when they are trying the same with the mother they don't bring the defibrillator with them - how dumb is that?
My suggestion - Don't waste your time watch some other apocalypse movie.