The Avenging Angels series, by A. W. Hart

[Werner]

One of several series published by Wolfpack Publishing is Avenging Angels, featuring a twin brother-sister team of teenage bounty hunters in the West in the years just after the Civil War. (A. W. Hart is a house pen name used for all the books in this series, which are by various authors.) Despite the teen protagonists, it's adult (albeit clean) fiction, not YA. There are 12 books in the series so far.

I've only read the seventh one, Avenging Angels: The Wine of Violence, written by my Goodreads friend (and our fellow group member) Charles Gramlich, and now the second one, Avenging Angels: Sinners' Gold, by Wayne D. Dundee. But I'd recommend both of these, and my wife Barb really liked both novels as well!