Hi, I'd like to ask some questions. Please let me know which are right or wrong plus your kind explanation. The sentences are :

1. It was five in the afternoon when she arrived, but by then the meeting had already been underway.
2. It was five in the afternoon when she arrived, but by then the meeting had still been underway.
3. It was five in the afternoon when she arrived, but until then the meeting had already been underway.
4. It was five in the afternoon when she arrived, but until then the meeting had still been underway.

5. It was five in the afternoon when she arrived, but by then the meeting was already underway.
6. It was five in the afternoon when she arrived, but by then the meeting was still underway.
7. It was five in the afternoon when she arrived, but until then the meeting was already underway.
8. It was five in the afternoon when she arrived, but until then the meeting was still underway.

9. By the time she arrives, they will have already been studying.
10. By the time she arrives, they will still have been studying.
11. Until she arrives home, they will have already been studying
12. Until she arrives home, they will have still been studying.

13. By the time she arrives, they will already be studying.
14. By the time she arrives, they will still be studying.
15. Until she arrives home, they will already be studying
16. Until she arrives home, they will still be studying.

Sorry for presenting all similar sentences in a dull list form. I hope you read them as I want to know the differences among them clearly.

Are these all acceptable in terms of TOEFL grammar?
Are they all acceptably used in real life English?