Genealogy research often is solving a mystery.
But it is not like the mysteries one sees on television or reads about in novels. The answers are usually the simplest explanation. The legal terminology may be convoluted, but the reality often is not. Generally speaking the easier possibility is usually what took place.
A correspondent had started research on a family using what records could easily be found online at no charge. Based on the limited items they were able to find, they had the great-grandfather having two relationships and children at the same time 100 miles apart. It made for a good dramatic story. The reality was much simpler. The “other wife” was actually the great-grandfather’s second wife and the “funny birth certificate” was actually one created after the great-grandfather married his second wife and legally adopted the child she had with her first husband.
Locate as many documents as you can and try to avoid creating a detailed intricate drama. Usually the easiest explanation is what took place. Usually.
Your relatives were not living in an episode of “Murder She Wrote.”