Good question, Karen!
A factor that might be assistance in trying to solve this question with autosomal DNA and a chromosome browser (simply matching in Ancestry is not specific enough): If you find descendants of the youngest siblings in each generation, you might find living family members whose DNA still contains an appreciable amount of the ancestors who were living that long ago. Remember that autosomal DNA recombines, and half of it is 'lost' in every generation. So if Mary and her siblings were having children from 1791 to 1819, as seems to be the case, that is almost a 30 year span - already a generation and a half right there. If you were able to find a few 80+ year old descendants of Mary and of her Bryan potential siblings and of her Ingram potential siblings, let's say born around 1940, that is 150 years ago. If those descendants are in an unbroken line of first-borns, 7 to 8 generations would have passed, and you really couldn't expect very many segments to still be staying together through that. But if you were able to find a few testers whose line is almost all the youngest children in the family, those 80-year-olds might only be 5 generations after your Mary, and there might be some chance that there might still be recognizable segments of DNA that could be matched. Check out this chart:
https://dnapainter.com/tools/sharedcmv4
On the other hand, there are going to be other factors that will make this DNA work difficult. One of the challenges will be finding potential testers who are not also related on other lines. Families who lived in small early settlements for a few generations often ended up being related to each other more than one way. Even if you find a match, you will have to trace all lines for all testers to rule out other possible inheritance paths for that segment...
You might also be able to do something with mtDNA if you are able to find all-female-line potential testers. If you have an unbroken female line from Mary the mother of Henry, and also were able to find all-female-line descendants of Mary Bryan's sisters and of Mary Ingram's sisters, the results cannot prove relationships but can rule out relationships.
Bear in mind that whether you are working with autosomal DNA or mitochondrial DNA, you need quite a few testers that all match to rule out unrecorded adoptions somewhere along the lines.
Sounds like a big project! But yes, there are ways DNA could be helpful!
Cheers
Shirlea
