Unlike Todo, I don’t think Choso is very likely to refer to someone as his brother unless there’s a literal familial connection. Without trying to be funny, I think his brotherly bonds tend to be much more about blood. So, with that being the case, I couldn’t really have him answer this question in the affirmitive.
However, I did have a crossover pairing I wanted to do with him. I’m not sure what exactly made me want to draw Choso with Envy. It might be just because I already had an FMA connection in my head due to Choso’s debut (and, in fact, I’m certain these two met when Envy tried to crash Ed’s debut shoot), or it might be they’re the only two males so far who don’t wear nail polish in canon but do in Studio (to the best of my knowledge). I do also kind of like the image of them painting their nails together. Whatever the case, though, it was a pairing I wanted to do and this Ask seemed like a good chance to do it while also addressing my reading of Choso’s brothers needing to be literal.