Ответ:
1. Jack is not sure if he will be in London next week.
2. If he goes to London next week, he will meet his cousin Mary.
3. If you don't change your plans for the coming summer, I'll go to the sea w/ you.
4. I don't know when I'll watch film but I really want to do it.
5. Please tell me when you'll be able to come and see us.