They don't look authentic to me. The writing on all of the phrases is identical, which means it was probably written by one person (rather than signed by many people, as is usually the case with WW2-era flags). Two of the flags have the same name on them: Hashimoto Kikuo. Its sort of unusual to see two flags with the same name on them. Usually the person going off to war would receive a flag from his school or his place of work, and it would be signed by his acquaintances. It's not impossible to see two flags with the same name, but it is highly unusual. (Did he receive two flags, take them both to war, then return with them both and sell them?). I find these items to be a bit suspicious.