that hasnt been stated either. the 20 fodders and the bros attempted coup are two entirely different events probably years apart. during the coup tobriama was left on the verge of death and defeated by kinkaku and ginkaku. stated multiple times. later on he sacrificed himself to distract the kinkaku squad, which were kumogakure shinobi, NOT s-rank mercenariesExactly,as i recall it has never been stated that it was the two brothers alone who severely injured Tobirama, it was said that a squad of 20 ELITE ninjas did it, meaning 2 things:
stated multiple times the bros fought alone and claimed sole responsibility for defeating him at the coup attempt2.Even if he did die due to those injuries it was actually those two brothers plus 18 others who killed Tobirama.But it wasn´t just the two brothers, there is a huge difference.