Old Aliens

Way back in the day a bunch of different types of people were kidnapped by aliens. The first part of the book deals with the survivors and some people they hadn't met before The second part is about the kidnappies. They are taken to an alien planet and plan am escape. They realize that the planet used to be filled with aliens but now there aren't many left. Eventually the humans kill the aliens but realize they are stuck on the planet The third part is from earth's point of view and are about the humans returning home after two hundred years or so. They had to advance their own technology till they could travel back The next part is the history of their advancement. They had to use alien technology to learn over the years how to make a ship to get them home. They also found out that the planet was dying and they would all die. They ended up taking home an alien body with them When they got home they have to deal with how different they are from the earthlings. Also they find out that aliens had hidden themselves as humans and their descendents were now scattered across the globe and no one knew why When they find the alien descendents they hear a story told generation to generation about their home planet. The kidnappies were meant to save the alien race as they were chosen for their skills