Guide on adding a new model, animation, and creature to HoMMV

What I mean is, when I open the basic skeletons from Heroes 5 in 3ds Max, they don't open as bones, but as helpers... although they look like bones....
P.S. Regarding your link - it's not easy to understand at first glance. Does it allow you to import a model and animation into the game without using Maya?

Yes, Maya is not needed. Read what I wrote - did I write all those words for nothing? I create a Helper instead of a bone, making it GLOBAL, and the GR2 exporter recognizes it as a bone based on the naming of the rigging elements. Disable the elements of the rig so that they don't end up in the final GR2 file.