But Jean (English name, like Jeannie) and Jean (French form of John) are entirely different names, with different pronunciations, that happen to share the same spelling.
Yep, my wife and I have the same middle name: Jean. I’m French and she’s British :)
I am curious how you define "entirely different", because where I am looking, all the names you mention have parallel etymologies, the same origins, and similar meanings. We find them with different pronounciations and many spellings, because of the regional languages spoken, but they were adopted into a multitude of languages from the same sources. So how do you consider them "entirely different"?