Here are the correct forms of the verbs for each sentence:

1. We’ll go out when the rain **stops**.
2. Miss Helen **will help** you if she **finishes** that letter tomorrow.
3. I **will come** and **see** you before I leave here.
4. I **will wait** until he if you **come** back tomorrow.
5. I **will send** you some postcards as soon as I **arrive** in London.
6. I’ll wait until he **finishes** his novel.
7. I **will give** her your letter if I **see** her tomorrow.
8. When you **go** into the office, Mr. John will be sitting at the front desk.
9. We **will wait** for you when you **get** back tomorrow.
10. If you **come** today, I **will work** at my desk in Room 12.
11. I **will give** her your letter when I **see** her tomorrow.
12. As you **go** back home, your children **will wait** at the front door.