I think they're great mannequins and not that stiff. Still if you take a look for example the man's back leg you can see that in the reference the leg is like a D but yours is like a C 😎 so these "mistakes" are maybe what stiffen or robotize your mannequins pose.

Hey Mila, When it comes to reducing the body to shapes, it's best to use simple shapes such as tubes, spheres and boxes. It makes it easier to make the body look 3 dimensional, and show perspective. I did a quick sketch to show you what I mean, I hope it helps :)