Perhaps you already have the answer to your query. I too have the same ancestors and am researching them. I have traced Henry to Jamestown, but now think that it is incorrect because of this Henry. I am thinking that there might be two Henry Mitchells since the dates are way off.
I have use as my source: "Thomas and William Branch of Henrico and Some of their Descendants" by William Clayton Torrence - Page 107 of 107-116.
According to the book, Henry Mitchell's parents are Henry Mitchell, Sr. and Tabitha Branch (which goes to the Jamestown Branches).
Any help out there would be greatly appreciated.