BSC LLB is an integrated dual degree program which covers BSc and law studies and therefore you can later do a PG course in law like LLM or any other PG course Msc..etc.. as per your interest.

yes you can apply after 12th class but the eligibility may differ college to college.

In India, BSC LLB colleges are less.
KIIT provides this course.
You can check the course and eligibility here .

Good luck!