There is only one arrangement possible.
See diagram. Follow the following steps.
1. Draw circle. Draw 8 small circles for seats around the circle.
2. Place F on the top, to start with. You could start at any other place too.
3. Place C as per given condition.
4. Place H as per given condition.
5. Marks the places not allowed for D.
6. Fill D in the only place possible.
7. A and E are together. That is only possible between H and C. So fill A and E as per rule.
8. Fill G to 2nd left of A , as per rule given.
9. B is filled between C and D, as that is the only place left.
Answers to questions
1. Arrangement is
ANTI clockwise from H : H A E C B D F G
Clock wise from H : H G F D B C E A
2. F is between G and D
3. We should find anti-clock wise CB , AE, GF, AH or we should find clock wise, BC, EA, FG or HA.
we find the pair EA.
4. anti clock wise -- see arrangement in part 1.
there is A. only one person.