I am putting a few guidelines with respect to your query relating to MNC job and the points would clarify your prevailing doubts.
1) Once, you have been selected for any MNC, the personnel department of the company would release a letter of your joining subject to your medical fitness by the medical board of the MNC company and your joining would be finalised upon the receipt of your medical fitness issued by the medical - board. The process would not take more than a month once you have been selected by the interview - board. In case of any delay beyond that, you may contact the personnel department of the company.
2) If any correspondance has been made to the HR department of the said company, you should have indicated your earliest confirmation of joining of the company since you are attempting the interviews of other companies as well and in the event of selection in any one of such companies, you could join the the job after receipt of final confirmation of the company.
3) Still you can intimate the MNC regarding your desire.
4) All MNC companies are in the habit of following the fair practices in respect of offering to appointment letter to the successful candidates irrespective of the sources from where you have been picked up. However, it may so happen that you may not get any appointment letter during the process of campus interview organised by your college. So it would be better to seek a further clarification from the said MNC company. To
5) You should not wait beyond three months for getting an appoint letter of a company. Better try for a new assignment.
6) Send your resume to Naukari.com or any related such companies so as to get the chances for any job of your liking.
7) You may try for additional certifications which can widen your job - prospects such as Oracle certifications through NIIT or APTECH. You can even join join for Java or C++ advanced courses. In case, you want to enhance your oral skill in English to impress the Interview - board, better join a reputed institute in this direction.