Diploma

There is no lateral entry abroad for engineering based on Diploma Engineering in India. I suggest you to complete degree in India and then for PG studies you can do overseas.

The eligibility criteria and admission details related to BCA of Symbiosis Institute of Computer Studies and Research, Pune are given below.
Eligibility criteria : Student passing XII from any stream or equivalent government approved diploma in Engineering/Technology with minimum 50% marks (45% for SC/ST candidates)
SELECTION PROCEDURE : Symbiosis Entrance Test Score, Personal Interaction and Writing Ability Test (PI-WAT)
So from above you are eligible. If you have completed you Engineering Diploma with minimum 50% of marks.

No, you can not join. As per the Lateral entry programme criteria, The student should pass in 3-year Diploma (respective Engineering stream) granted by the State Board of Technical Examination with minimum 45% aggregate marks or equivalent.
So, for B.Tech CSE lateral admission, the Candidate should have passed a Diploma in Computer Engineering.

You are completely eligible to for B.Ed education. Minimum eligibility requirement is 50-55%.

Following are the few universities offering B.Sc. OT lateral admission as given below. Please go though with their website for more details.
1. Parul University, Vadodara (https://www.paruluniversity.ac.in/)
2. SGT University, Gurgaon (https://sgtuniversity.ac.in/)

No, you can't write. DCET is only for students studied in Karnataka.