Could you correct the mistakes, please?

1. Let’s hold a conference after we've had have a dinner.
2. I can’t work until I have breakfast.
3. We were waiting at the airport until they came.
4. Sally told me about her engagement when she was here.
5. I’ll come as soon as I finish my work.
6. I’m going to London next week. I hope to meet Tom while I’m there.
7. He won’t come home until they return.
8. They had gone went while I was talking with the doctor.
9. I was informed about this at on the day when I came to Moscow.
10. By the time he came the police had left this place.
11. I’ll bring you this book next time when I come.
12. They hadn't heard didn’t hear from him any news from him  since he had left Russia.

Could you correct mistakes, please?

1. Let’s hold a conference after we have had a dinner.

2. I can’t work until I have had breakfast.
3. We were waiting at the airport until they came. Arrived. (Came is correct, but arrived is better)
4. Sally told me about her engagement when she was here.
5. I’ll come as soon as I finish my work.
6. I’m going to London next week. I hope to meet Tom while I’m there.
7. He won’t come home until they return.
8. They had went while I was talking with the doctor.
9. I was informed about this at the day when I came I went to Moscow.
10. By the time he came, the police had left this place. (again, i think it is better to use the word arrived in this context. So, the following would be better - By the time he arrived, the police had left.
11. I’ll bring you this book next time when I come.
12. They didn’t hear from him hadn't heard any news from him, since he had left Russia.

8. They had gone while I was talking with the doctor.
9. I was informed about this the day  I came to Moscow.
10. By the time he came the police had left this place.
11. I’ll bring you this book next time I come.
12. They didn’t hear any news  from himsince he had left Russia.