1. When I saw Nick, he was writing a letter.
2. At 2 o'clock my mother Fiona was cooking soup.
3. The father wasn't sleeping when little Freddie opened the door.
4. At 10 o'clock, Samantha was doing homework.
5. When the old teacher came in, the children were talking.
(Чёрным курсивом выделил время Past Continuous)