will update the question with the number 9 to the thread.
Name of the recipient (sister) could be Motra (Мотра) - maybe an another form of Matrona/ Матрона - wiki
The blue 9 is probably some sort of marking from soviet secret services/archive, thanks a lot for this observation, it might help understanding better how these postcards were collected and stored originally
Numbers written in blue crayon exactly like these on postcards and letters in Germany usually indicated postage due on insufficiently prepaid mail (no/not enough stamps). But usually they were accomplished with a red stamp „Nachgebühr“ and these postcards were already prepaid, so I think it’s unlikely here.
I wanted to mention it nevertheless just in case it helps somehow with understanding more about the postcards.