Hi candidate,
I think in all engineering college they teach basic programming in first year. So you can learn basics of programming there. If you want to learn on your own in this quarantine then you can buy some udemy course and improve your coding skills. I think should make this lockdown useful and learn something.

Hope this helps

Yes you can opt Computer Science Engineering in your Btech in Spite of not having Computer in your 12th.

This is not a problem as i have seen various students going for CSE after studying Eco Science or bio Science.

Don't worry about the basics as you will be taught from the basics in your Engineering Course.

From basic C.