How to create a Multistep form?

I cannot understand your problem. Why don't you take a screenshot?
multistep simple lable(group parent)
- step 1 (group child)
--- field 1
--- field 2
- step 2 (group child)
----field 3

Sure, I'll add the steps I tried and screenshots.

It would be nice with some basic documentation. Perhaps it can be added in a README.md file i the module, or a documentation page?

I now understand why it's not working. Instead of having multiple field groups multistep, you should make one field group multistep with another field group foreach steps, it works like form API.
If you could provide documentation, that would be appreciated, as I am short on time.

Thanks for the tip, it works better now, and the steps work. But the Status, Revision, and URL alias fields are shown at the bottom ...