Diploma

Yes, it is possible but you have to do hard work because after two years you have to face maths which will be difficult for you.

Following is the link where you can find many colleges in Andhra Pradesh. Find a good one according to your elegibility: https://www.shiksha.com/engineering/colleges/colleges-india?rf=filters&ts=34955545&tf=5034473&ct[]=702&ct[]=40&bc[]=10&ss[]=sp_10&uaf[]=location.

Yes, of course, there are many colleges offering distance education. You can also do distance education in some of the top colleges in India. I would suggest you to visit Shiksha.com and find the right college for your distance education.

The following are few of good automobile institutes in Pune:
RMDIT, Pune
Kohinoor Tech. Institute
DPCOE Pune
Sinhagad Academy of engineering, Pune
Government college of engineering and research
Government Polytechnic Awasari are some of the options. There are some other options like these as well.

According to my point of view, you should choose AMIE with mechanical engineering and if you continue your studies then you can choose M.Tech with polymer which is totally different from private B.Tech colleges.