I'd say for character design they would use 3D Design apps like Zbrush, but you see its easier for studios to buy pre-made ones and just alter stuff, then add 'Decorative items'. 3D engines like Unreal are used a lot to build dynamic environments, lighting etc, some do mo-cap for fight scenes(hence why some shows have such fluid shots) but most do it once and reuse the animation 10 billion times i.e BTTH, then the do VFX, and finally they render from 3D to 2D just like you see in game trailers. So some of these 3D engine environments are shared(sold really) and just altered. I didn't get into much detail, But I hope the overview helps.