Though I can't yet be sure about the details concerning Mathias Ambrose, my mother-in-law's third great-grandfather, I can be much more confident about the information I've gathered about his daughter Elizabeth. Elizabeth Ambrose, taking her place in my mother-in-law's direct line of ancestors, was likely born in the same location where we last saw her father: Bedford County in Pennsylvania. However, at an as yet unknown date, Elizabeth became the bride of a man whose brother married Elizabeth's sister Susannah. Thus, my mother-in-law's ancestors became party to that relationship sometimes called double cousins.
The two brides—Elizabeth and Susannah—were married to Joseph and John Henry Flowers, two brothers who also were born in Pennsylvania. I have yet to locate documentation providing the date for either the wedding of Elizabeth and Joseph, or Susannah and John Henry, but some circumstantial evidence does lead to surmising those dates, as well as when the couples left Pennsylvania for property in Ohio.
Since the sisters' father mentioned them by their married names in his will, dated in 1804, it is safe to say their weddings occurred before 1804. Besides that, we can look to the births of the eldest children of each sibling.
Susannah, having married the eldest of the two Flowers brothers, may have been married first. The oldest of her children that I have on record, Mathias, was named after his maternal grandfather. His year of birth—in Pennsylvania—has been given as either 1802 or 1803. Still, it is possible that he was not Susannah's firstborn, thus her marriage could have occurred a few years earlier.
Likewise, I can't yet be sure of pinning Elizabeth's wedding date based on her oldest child's birth date. There may have been an older child I have yet to discover.
Two of Elizabeth's eldest children—John, born about 1804, and Joseph, born in 1811—in later years gave their place of birth as Pennsylvania, while some notes about the third-born child, Thomas, suggest he was born in Ohio. In an 1883 publication, History of Fairfield and Perry Counties, Ohio, a brief biographical sketch for Thomas Flowers gave his place of birth as Muskingum County, Ohio. While that book also stated Thomas' date of birth was in 1814, his headstone shows his date of birth as November 12, 1812. No matter which date is correct, though, we can assume his parents still were in Pennsylvania until that point.
I'm still attempting to find an online source for the two Flowers marriage records. While the FamilySearch wiki for Bedford County indicates there is a file for marriage records, for some reason, I have not been able to open that collection yet. Nor does it seem likely that we'll be as fortunate with grandchildren's biographical sketches naming their pioneer ancestor like we saw with our quest last month to discover more on Lyman Jackson. Still, revisiting some old notes saved from past explorations on this puzzle about Mathias Ambrose, I realize it wouldn't hurt to pull that material out for review once again.