Hello Sir,
We are team of Professional 3d Artist and Game Developers , we have worked on many projects you can check our profile for our reviews from all over the world, the next thing is that we work on unity and unreal engine 4, they are both are great platforms for the games, as per checking your attached brief, i think for your required performance and features Unreal engine will be best for your game project, in that engine we have more possibilities to make a perfect adventure game with eye pooping graphics, give us a chance we will do perfect work for you with personal opinions too..
Thanks, Jas3d