Mechanical Engineering

Yes, mechanical students hold eligibility to pursue M.tech in Aerospace Engineering. Some of the reputed colleges to pursue this course include :
IIT Guwahati
Indian institute of Aeronautics in Patna,
IIT Mumbai VSM Aerospace Academy of Aerospace and Engineering Indian institute of Aviation Technology UPES Dehradun You can target these as per your preferred location. Admission & Eligibility criteria you can check on websites of respective institutes. Good luck :)

If you are locality of chhattisgarh n don banana to relocate CSIT or Rungta is good.But RiTEE is also good one. Rungta passouts are working abroad also.

Yes especialised courses are there for diploma holders in fire and safety. Duration range from 6 months to 1 year.
PG DIPLOMA IN FIRE SAFETY ENGINEERING course is offered by National safety council. Chhena.
All institutes have some good and bad areas. some lacks something. so depending upon your ease you can choose one of them. The word "Ease" itself has vast meaning.

Hi
The MS offered in most of the universities abroad might be specialization in mechanical where you may study about both production and process planning as these are basically the job profiles in industry.

I think you can pick up a reputed state college or even a NIT. Mechanical would be a good branch if you have personal interest in that kind of work.

You might try in Amity university noida, or Galgotias university greater noida, Jaypee , or SRM ncr campus.