Explanation:
1. not only/ but also in (a); either my sister or my brother in (b).2. has in (a); I have interest in neither playing nor leading in (b).
3. Both are correct.
4. hardly had he
5. the better it is
6. talking about either his strengths or his weaknesses.
7. Both are correct.
8. on or by the 15th
10. such a poor is wrong