There is one error in each sentence
1. At the night, my family and I used to chat until we went to bed.
2. Mary is my grandmother, she is 70 years old.
3. I am strongly agree that the future of Hong Kong is good.
4. I am looking for a girl, who is honest and open-minded.
5. Despite the main was heavy, we went to see the firework display.
6. I believe that if the Government does so, the problem will be solve soon.
7. I hate a person a person does not tell me the truth.