Yes, you can do law even after doing 12th in PCM.

it won't matter at all but you should have a keen interest in the law field and want to excel as a lawyer.

you can give CLAT held by national law universities and can choose a 5year law or 3-year law.

being in any stream in 11 and 12th won't matter if your scope is doing Law.

You can check the below links for the Clat syllabus and all and score excellently in exams:

https://law.careers360.com/articles/clat-exam-pattern

Hope this helps you