Large amounts of Tatiana's diaries are in "Sisters of Mercy", so I guess for Russians her handwriting isn't impossible to transliterate.
Confirming, according to sisters of mercy, there are indeed 3 extant diaries of Maria's. Her letters indeed have more interest, like them all, the diaries are more about what they did rather than what they felt. No diaries of Anastasia's available, at least not at GARF.