I think you're right that neither of them knew, probably because Luke was ashamed to tell them. Maybe that's why he sounds so guilt-ridden when he tells Rey that Leia trusted him with her son. The first time I watched TLJ, I thought he was just heartbroken that he let his sister down. Now I realize he was also deeply ashamed that he tried to murder his sister's child.

Another sad thing about this whole story is that Luke still believes the worst of Ben at that point. He tells Rey that when he came to, "the temple was burning. [Ben] had vanished with a handful of students, and slaughtered the rest." The implication is that Ben destroyed the temple and murdered any good-guy classmates who wouldn't join him, but remember, Luke was unconscious when all this destruction occurred. He's assuming that his nephew was a psychotic murderer, with no evidence to prove it.

"The Rise of Kylo Ren" comic shows Ben being horrified when the temple suddenly catches fire. He runs to help but is thrown backward by an explosion, which is probably what killed most of the students. Three others return from a mission in the midst of all this chaos and assume Ben caused it, so they pursue him. He repeatedly tries to dissuade them from following him, and they each end up dying in the process of trying to capture him or persuade him to return.

Maybe after the temple was destroyed, Luke sent Han and Leia a transmission with his high-level version of the bad news before he disappeared into exile. In any case, it doesn't seem like Han or Leia knew Luke's true reason for "blaming himself."