The "sada" kanji in Sadako Sasaki's name means "happiness".
The "sada" kanji in
Princess Kujo Sadako's name has several meanings, some of them are "season", "verse", "honor" and "tune".
And the "sada" kanji in both Sadako Ogata and Sadako Yamamura's names is the one that means "chaste". It can also mean "righteousness" and "upright".