Karen,
Until about the middle of the 18th century, the Welsh named children based on the father's given name as a surname. This patronymic naming system is explained on a number of Web sites. A brief explanation is at:
http://www.bbc.co.uk/wales/history/sites/themes/society/fami... .
Apparently, Emanuel Jones named his son David Emanuel in accordance with the patronymic system but David Emanuel, Sr. and wife named their children in anglicised form. Some of this carries into names such as Johnson, derived from "son of John."
I have not seen the Will of Emanuel Jones on the Internet. I have a digital photograph of an image of the original that is very difficult to read. I will look into doing a transcription, but it may take awhile. Because of my job, I only have time for genealogy on weekends.
If you wish to correspond directly, my e-mail address is
wemanuel@thenandchange.org.
Regards,
Bill Emanuel