Thank you, Victoria. I'm blushing.
So in my digging around last night, I discovered that William almost certainly never left California. He was admitted to a hospital there in 1876, and his intake history says he'd been there since 1858. Here's William's profile.
So that's one brother checked off of my list.
As for Theodorick, I know he was in El Dorado County, California in 1860 and Calaveras County, California in 1867, making it likely that he was nowhere near Texas, either.
A third brother, Robert (no fancy middle name) who was born in Springfield, Missouri in about 1841, falls off of the genealogical radar after the 1860 census. He isn't even mentioned in any of his father's or brother's biographies. I had to admit defeat for him.