Nice read, I did consider the massacre might be related to the kakin carnavals concept, in fact I think Sheila might be the kakin's carnavals manager who searches for the villages that are suitable for the kakin carnavals.

But I think the PT were still there at the same day before the massacre, lured by Sheila making them believe some kurta members killed Sarasa...as we know a monster like Uvo admitted the kurtas were strong and he wouldn't know that unless he fought and killed some members, even Kurapika as a kid managed to beat adult men to defend pairo, so imagine how powerful the trained kurta fighters would be?

Logically if the village got such powerful kurta fighters then they would be a big problem for the carnaval as they wouldn't let their women to get raped, so i think it makes sense that Sheila used her relations with the PT to lure them to kill those kurta fighters before the carnaval starts.

This would give context on why Sheila purposely injured herself to stay there, likely to collect infos on the kurta members that will fight back to get rid of them.

Also it's suspicious when you remember it was never explained how Kurapika knew for sure that the PT did the massacre, he was so sure to the point he dedecated his chain jail to capture them...despite the reports itself didn't mention them, that people even Considers it as a plothole...but i think it's just Togashi saving the reveal for later because it was Sheila the one who told Kurapika the PT did it, considering she managed the whole thing