Very few family myths or legends have been passed down in my family, so I haven't had many stories to investigate or confirm. I have, though, been able to confirm a few stories or at least confirm some of the facts in the few stories that my family has.
On my father's side, there was a story that one of our ancestors had served in the Civil War. I was able to confirm that this story was true and in addition to my ancestor, his brother-in-laws , his wife's uncle and possible at least two possible brothers also served. (I haven't been able to completely verify yet that these two other men living in the same county are my ancestor's brothers. I'm still doing research on whether are his brothers.)
Another story from my father's side claims that someone in the family became a cattle-rustler, but I haven't proven that story yet.
On my mother's side, one family story claims that my great-grandfather was the youngest of thirteen children and that he went to live with a married siblings after his parents died. This older sibling mistreated him to the point that he ran away at thirteen and joined the crew of a ship. I've been able to confirm that he ended up living in the household of his older, married brother, but I haven't been able to confirm the part about working on a ship. I don't know how true that portion is. Also, I've only been able to find about ten other siblings, so it may be possible that he was the youngest to thirteen.
These are just a couple of the few stories that were passed down. For most of the few family traditions that my family has, I have not yet confirmed or disproved them. I'm still searching.