If you are considering to create 3D animations of just about anything, Blender may be the program to use. It is free and multi-platform and was engineered for just that purpose.
Because it is a powerful program, one would have to have a reasonably powerful computer with a strong emphasis on a powerful graphics card. It will run on a less-powerful machine, but you will find complex animations as you have described will be slow to render and to process.
With respect to your last question, you may find Blender resources specific to your requirements, but they are more likely to be models that would require you to "install" armatures in order to provide for "lifelike" or even awkward movements.
You may also find that the internet and YouTube and other video resources exist with comprehensive tutorials. Blender is known to create wonderful animations, but also is known to have a substantial learning curve. There is also Blender SE for specific questions that arise during your learning experience. Perusing the SE in advance of beginning the educational climb is also a valuable exercise.
If you are able to devote the time to learn the program, your results will be limited only to your imagination.