MMS Eligibility

I didn't understand what you want to know, your GMAT query and JBIMS have no connection. If you are looking for MMS 19-21 batch with JBIMS, then you need to give CET buddy,

It does not matter you have engineering, B.Sc or B.Com degree, all are eligible to take the exam and prove their potential. If you are capable of getting that one seat than it is definitely good for you to join JBIMS because you have proved your potential to compete by securing that seat. For your knowledge, yes students over here are of great mix, some from B.Sc. B.Com LL.B.Pharma, etc. Believe in your potential and never doubt your degree as ever degree gives you certain skills which upscale you from others.
You need to be hitting top 40th rank in MHT CET for open category.
Hope I helped!

MAT score are not acceptable; placements of MMS are almost 100 percent.

For MMS program, you have to go through the CAP process and the process has a major weight to the CET exam. But for PGDM, you have a fair chance of conversion but your selection will depend on your performance in GD PI.
Good Luck.

For MMS you can visit official dte website
For PGDM, GD/PI rounds will take place in MET Mumbai campus

Yes, you can get admission in WE School - Prin L N Welingkar Institute of Management Development and Research, percentile above 80 are accepted.

It is difficult to say, you can surely get admission, because only few seats are available in SIES of All India Level seats and that require percentile above 98 in any of the National level entrance for MBA.

There is no eligibility criteria based on 10th and 12th score. Your graduation percentage should be above 50% (45% for backward classes).