rewatching season 3, i can finally comfortably assert that BoCo and Edward are not the same character.
a thread:

while edward has always been bill and ben’s dad, boco can be seen more as their second adoptive dad. BoCo undergoes subtle character development from “the diseasel” to “wrong road”. he starts out very weary of bill and ben, hesitant to get involved wthem in a way edward never was

while edward always wanted to look after bill and ben, boco was reluctant. over time he learns to understand them and, by wrong road, even gets involved in a plan to teach them a lesson.

are boco and edward massively different characters? no. but there are important, SUBTLE ways that boco is distinct from edward. boco is a gentle giant that prefers to keep to himself, who changes into a loving and patient co-guardian of the twins across several stories.

if all the boco stories were one railway series book, perhaps it would be more obvious how his character changes over time. but instead it happens subtly over a long period of time, which naturally leads to people overlooking it entirely.

in conclusion, boco has a distinct personality, it’s just easy to overlook.