I saw a post recently in a group on Facebook asking if she and her husband shared matches does that mean they were related. The answer of course is possibly, but not necessarily. I am going to use some of my family as an example.
Both my mother and my father have roots that go back to Colonial Maryland in Prince George and Queen Mary's county. For my father this is the Pyburns, for my mother it is her Traherns. Both families end up in the same area of Virginia, the Pyburns by the mid 18th century show up in records for Lunenburg and Bedford and the Traherns are in Pittsylvania county (formed from Lunenburg) by the 1780's. Additionally two collateral families who marry into my mother's family (not my direct line) take this same path, the Brashears and the Walker (Sylvanius Walker and Tandy family) family.
Things get even a bit more interesting when you look at the Pyburn family. My direct line arrives in Tensaw in 1784 where they end up being neighbors to my ancestor Peggy and her husband Charles Juzan. Well as neighborly as the wilderness was at that time. Turns out that Peggy goes on to marry James Trahern and my line is developed. Peggy and her husband Charles Juzan are the godparents of at least one child of Adam Hollinger and his wife Mary Josephine Juzan. One of their sons marries Teresa Innerarity, the illegitimate daughter of Mary Pyburn and James Innerarity. Thus relatives I have in my Juzan line share relatives in common with my Dad.
Whenever I see a Brunson, Bronson or Brownson before 1810 I know that inevitably the line comes from one of two brothers who arrived in Connecticut in the 17th century. The same goes for the Copelands of Virginia, a name I see often enough in tree's for DNA matches of my mother, but oddly not for my father who is a Copeland. Funny how DNA works that way. That's not to say there isn't a handful of folks with small matches to both my parents, I just haven't figured those out yet.
If I start to talk about relatives on Dad's side, well it starts to look like I have a straight family tree. I don't, I don't even have cousins marrying cousins in my direct line in all the information I know about, (the closest is second cousins and only one of those), but we do have some first cousin marriages in the family. With Dad though, it's more that his family has lived in the same place for over 200 years. After a while, you just are related to about half the county who also descends from people who have been in the same place for 200 years. Which is why a recent DNA match matches my dad in two places, one from a match from his maternal grandmother, and the other, to a match through his maternal grandmother. Neither of us comes from consanguinity, we just come from families with a long history in the panhandle.
Take that in account with some of the rather large families Dad connects with, I mean he has one ancestor with over 100 grandchildren, 28 coming from my direct ancestor alone, and then make him a relative of another family who had 12 kids, and you get the picture. Before long you are kin to everyone, you just need a map to figure it out.
The funny thing is, Dad's family is so close and intertwined while my Mom's, aside from the Choctaw part, is not at all. And yet, she has some of the largest DNA matches with 4th through 6th cousins, and heck, sometimes with Dad it seems as if we are lucky to get a small one at 4.
So my point is, DNA is grand, but you have to take it in hand with genealogy and a grain of salt. After all, it's all relative.