Sorry can't help you, but interested in any research you may have, as my ancestors were Blackwells from Medbourne. Earliest I have is William Blackwell b. 1767 approx and died 1850. Married Hannah b. 1769 and died 1836. Son John Blackwell born 1795. So possible that William was offspring or, less likely, sibling of Mary.
Any information you have would be appreciated.
Johnny B