Science

I think you cannot get admission in current session. For admission, the current session result will considered and as per rules candidate must have passed 12th with PCM with 50% of aggregate marks and 50% aggregate overall marks. However, you can apply for next NATA, scheduled to be held in July-2019.

Yes, you can. However, based on your syllabus only the course director can take this decision after seeing the papers you have covered in your engineering Diploma. If you have done this Diploma after 12th, you will be considered easily. If you have done 10th and then Diploma, it will be difficult to confirm this.

Yes, after completing 12th class studies, you can take admission in BBA. There are too many career options available for 12th science (biology) students. You can check some of the most popular career options here: http://articles.abilogic.com/196120/topmost-career-options-12th-science.html
I hope it will help you to choose the right direction for your career. For colleges go through this link:
https://www.shiksha.com/bba/colleges/bba-colleges-delhi-ncr

Here is the link to help you-
https://www.shiksha.com/university/patna-university/patna-university-blet-exam-question-papers

The refund process varies from college to college. In most of the colleges, fees is non-refundable. You need to check with the college about its refund policy after admission.

No, you cannot apply for that. You should complete your B.Sc degree first in order to pursue M.Sc degree.

To get an answer to your question, I would advise you to please get in touch with the college specifically. Here are the contact details for you, in this link-
http://www.ccsuniversity.ac.in/web/Contact-us.htm
Or write at registrar@ccsuniversity.ac.in