When you export a branch of your family tree FTM the Export Branch Wizard automatically filters the project to relatives (ancestors and descendents) of the selected person and does not include the ancestors of spouses
Initially I was frustrated by that restriction, but after testing I finally understand why that is necessary.
I am NOT a genealogist and my Family Tree is probably an excellent example of what a real genealogist would NOT do. So please avoid making some of my mistakes. The size and content of my tree is an prime example of not planning ahead.
I have built my Family Tree with one of my grandchildren in mind. He is the root person on that tree and I have diligently located and included in his tree everyone I can find that is some how related to him. Consequently over the years I have created a monster that I am having extreme difficulty in managing.
He has deep family roots connecting him to ancient times on multiple sides of the family. He is connected to princes and kings from several different family lines. As a result his tree is not at all shaped like a tree but instead is more wheel shaped and the spokes of that wheel connect him multiple times to individuals and back around a different path back to himself.
This is exactly why the branch export does not include the ancestors of spouses. For if it did, any export of a branch would likely result in the export of the entire database. That would hardly be helpful.
Exporting a branch does not remove those individuals from the source database and having that capability would allow me to pare off some branches into separate files and begin to whittle the large database down to size.
At the moment I am stymied and seem to be faced with only one alternative; the brute force solution. What I mean is to duplicate the monster and then family by family delete those individuals I do not want in that new tree. I have done this with one branch and the pain level I experienced was not pleasant and because I am human and make mistakes I am quite sure that I removed familys that I should not have. So my new tree is probably already corrupted by my errors.