My husband's line descends from a Marion Francis Bowen, born in Kentucky in 1833.
He married Sarah Elizabeth Means(b.1841 in MO) in Dekalb County , MO in 1858. They had 13 children.

His brother, James M, born in Kentucky in 1825 married Sarah's sister Mary Ann "Polly" Means in Missouri and they had 14 children.
Since families were so large back then, I'm sure they had many siblings, but I have no knowledge of them so perhaps your Andrew and William could be siblings.

I have information that their father was Webb Bowen and his father Thomas Jefferson Bowen, but I don't know how accurate that is. My husband pulled it from another person's research .
I don't know if these brothers could be connected to your Bowen or not, but putting the information out there in case someone else has information. Maybe you've found out more since you posted this quite some time ago?