how to use DNA to help solve a brick wall

[expatmutt]

I have a lot of experience with paper genealogy, but very little with DNA. I am hoping someone can give me an idea where to start with this problem.

My father's line is easily confirmed by DNA matches going back to his ggg grandfather. For various reasons, though, I think his gggg grandfather is not who he is supposed to be.

One reason is that my father has NO matches that make sense beyond that point. There are several surnames--not uncommon ones--that I should be seeing in his matches that never come up. And, there are several recurring surnames that do not match my paper trail. From physical descriptions I have for the ggg grandfather, his presumed half-brother, and his presumed uncle, he doesn't sound like he looked at all like the rest of the family. (He was a full foot taller than his half-brother and blonde and blue eyed while they were described as dark.) And he also doesn't seem to have had much to do with his presumed father. I wonder if he may have been a stepchild or an orphaned relative they took in.

Unfortunately, I have had much better luck matching up with his relatives on ancestry.com. Which doesn't have any of the tools that FTDNA has for making sense of matches.

I am hoping that I can use DNA to narrow down the search a bit. I do know when and where the ggg grandfather was born, so that's a start.

What would you do under the circumstances to narrow the field for potential fathers (or mothers) of this person?

Thanks.

[JohnG]

Which tests have been done? Y chromosome? Family Finder?

If Y, you would expect the surnames to group somehow. I have one line that goes back to common ancestors in the late 1700s and then the next closest matches have a different surname. And then more distant matches have a third surname.

If Family Finder with a good paper trail, I have tracked down 4th and 5th distant cousins from paper and internet trees and gotten them to test. Also one half 4th cousin where there was a possible illegitimacy. So far all matched. But testing those distant cousins added confirmation. I should say I had several nearer relatives test so we lowered the odds of no match.

[expatmutt]

My dad did the Family Finder and Y-67 tests on FTDNA. I've also uploaded his results to ySearch and GEDmatch.

He has hundreds of matches but not one single match with his surname (Bembry). Even the matches I found on Ancestry are female descendants of his ggg grandfather.

So, would you suggest combining all the matches from all the services somehow and looking for patterns? Maybe a spreadsheet? How would I then proceed to use DNA to narrow it down further, if that's possible?

I have added his kit to the Grant Y DNA project, because I saw a few Grant matches, and he does fit in, but it could be hundreds of years ago. I am much more interested in the family history in the 18th and early 19th centuries--how they came to the U.S., that sort of thing.