Thanks to null and leslie.
Two of my chins( MaMa, grey, 4 years old, Female and ChaCha, 3 years old, Male) have been with me for almost two years. Cha Cha is very grumpy, he not just bit me and my husband, but also the vet and the vet assistant. The vet said he has never seen such a bad temper chin before. He said Cha Cha has mental problem. It is too nervious.
MaMa is single-armed because she was very active and trapped her arm between the wire grid( i don't know how it happened exactly, it was raised by my friend before). She doesn't want to share with others.
Another two are Snowball(pink white, 4 months old, Male) and P( 5 months old, female, half grey helf white, MaMa's girl) live together. I raised P since she borned then i bought Snowball back to stay with her a month ago. Snowball bit me when i first met him at the pet shop. Despite he bit, he looked so beautiful and had the colour i longed for, besides, the shop assistant said snowball bites because he is hungry( i wonder why i am so stupid to believe such bullpoo) so i bought him home. Snowball was first lived with MaMa and P. But because MaMa bit and hit him, he lost much fur, i seperated MaMa from P and him. Somehow, i think snowball bites me for curiosity instead of bad intention. It like to sniff my finger. After that, it will bite me. Though that didn't make me bleed, i don't like this kind of behaviour.
For P, she is a fast runner, i can't get near her....
So, for my situation, can anyone give me some more advice cos i find that local hong kong have little knowledge about chin, even the pet shop assistants, they are saleperson only, they even give false information!!