1. He wrote to her several times a week when they were engaged.
Q: How often did he write to her when they were engaged? How often did he write to her
2. She says that we should get him a gift voucher.
Q: What does she say we should get him?
3. He likes to visit his grandmother on Sundays.
Q: Who does he like to visit to visit on Sundays?
4. They make glass by melting sand.
Q: How do they make glass?
5. She says that Molly is her favourite colleague.
Q: Who does she say is her favourite colleague?
6. Julia Roberts is his favourite actor.
Q: Who is his favourite actor?
7. She said that the others would be arriving at half past seven. (do not use ‘when')
Q: What time did she say the others would be arriving?
8. They have three children.
Q: How many children do they have?
9. She became a brain surgeon when she grew up.
Q: What did she become when she grew up?
10. They spend time with their kids on Sundays.
Q: What do they do on Sundays?
Phrase 3: In a very formal style, ‘whom' would also be possible here: ‘Whom does he like to visit...'. In contemporary English, however, ‘who' is much more common here.