We saw them drive in at the beginning with the other Autobots but that was the only time we saw them. So just for fun, what do you think they were doing during the course of the movie? They were obviously going on their own missions in the beginning. Probably mischievious kinds of things like graffitti on landmarks and whatever. Then after they were called back to base, they were instructed to stay there on reserve since things were going down. They were probably used for training exercises or scientific experiments to find new weaknesses for Transformers. Then when Sentinel went crazy, that is probably when he killed them off screen. In fact, maybe when we saw that random explosion of debris flying out of the hanger, that was Twin parts since they tried to defend their human allies. They obviously were killed because they weren't deported as two of the nine.