Here are the completed sentences based on the provided structure:

1. Mary **is playing** piano while her parents **are watching** TV.
2. She **is painting** a picture while her brother **is doing** his homework.
3. Jane **is baking** a cake while her father **is decorating** the house.
4. They **are exploring** city streets and **taking** photographs all day.
5. My sister **is playing** badminton while my brother **is flying** a kite.
6. Ngoe **had** a meeting at 9 a.m. last Wednesday.
7. Quang **read** a science book all morning.
8. He **chatted** with friends online at 10 p.m. yesterday.