Lateral entry

No, Banasthali University does not allow admissions in second year. If you want admission for B.Com, you will have to repeat First year.

Yes, you can surely join BE in robotics and automation after Diploma in mechatronics.
B.Tech/BE through lateral entry (direct second year admission) will be best for you, you have to appear for LEET examination to get a good college.

Yes, you can surely join BE in robotics and automation after Diploma in mechatronics.
B.Tech/BE through lateral entry (direct second year admission) will be best for you, you have to appear for LEET examination to get a good college.

Yes, of course. For admission in JGEC and KGEC, you don't need to complete class 12th. But, for JU you need to have passed Class 12th.

For MCA, candidate must pass in BCA/ B.Sc (IT/CS)/Bachelor's degree in relevant discipline with minimum 50% marks.

No, there is no disadvantage at all, in fact it will save your crucial one year, as MCA lateral entry is a two year course.

Lateral entry mechanical engineering course is not there at MIT-Pune, check out the list of courses below:
https://www.shiksha.com/college/Maharashtra-institute-of-technology-mit-kothrud-Pune-23583/courses/be-btech-bc?ct[]=174&lo[]=545 (Copy paste the entire link on the browser).

Some of the most popular colleges are listed below:
1. Delhi Technological University.
2. Punjab University - Chandigarh.
3. Manipal institute of Technology, Karnataka.
4. Netaji Subhash Engineering College, Kolkata.
5. Jamia Millia Islamia.

Hello Kaustubh, the number of seats available for lateral admissions is not known in advance. These are normally dependent on the number of students who pass or fail after taking admission in the first year of four year degree course and also on the supernumerary seats sanctioned by AICTE. As far as the Government of Maharashtra is concerned there is a well laid out web page which will give you all the required information about this issue. I am attaching this link here for your ready reference.
https://dse18.dtemaharashtra.org/dse18/index.php/hp_controller/eligibility.
Best wishes to you.

It depends upon the institution you are opting.