These names are mainly called by family, or close friends. Some nicknames can be insulting if you do not know the person. Example, Misha is common, but if you called a person Miska then they can take it as insult.Olga was often called 'Olya' by her sisters I think
Tatiana was 'Tatia' or 'Tanya'
Maria was 'Mashka', "Masha" or 'Marie'...and even sometimes 'Littlie Bow Wow' (her sisters made this one up, I'm sure) - Masha is more common, Mashka used generally among family
Anastasia was 'Nastya' or "Shvizvik" (spelling?) Shvizik - its like saying joker
Alexander III was called 'Sasha' (This nickname was/is also used as a nickname for Alexandra) Shura is more common for female, Sasha is generally for males
Alexander = Can be either "Sandro" or "Sasha"
George= "Georgy" or "Goggie"
Xenia= "Malenkaya" perhaps by MF.
Olga = "Olya" or "Olishka" perhaps.