obviously the school does not want to take this responsibility too...
If I were you, I will just move out quietly without letting anyone knows. Cut that 99 and this b6 little bitch off. Of course your 62 will be in a bit of trouble, but it is his to solve. They have already put you 2 in such big mess, it is time for them to fix. Not yours, darling!
If 99 keeps calling you, just tell her your C6 is about to 脫離母子關係, it is just because she has pushed everyone to the limit! (or is already off the limit!!!) Or just throw the phone to your C6, ask your C6 to tell her this "news"! Of course it is just a threat. If she does not step back and "kindly ask her friend to go back to China", you guys will take further actions. She also needs to know by 脫離母子關係, it also means you will put this case to court, she will never be able to set foot in the Oz otherwise she will get arrested. She will never be able to see her son nevertheless the grandkids (well, now there is 1, but I m sure there will be more!!) ever again.