Adding to that, when you trade on behalf of a coporate body (a LLC is treated as a person in eyes of law), you need to have an investment advisor and NISM certified dealer terminal atleast to make it legal.
The PVT company thing works legally only for one person company where you are the sole proprieter. Anything else is potentially a violation including the NBFC norm I think. If you traded on demat of others based on advise given by LLC, then its advisory income which is outside the NBFC norm. But for that you need to have IA and NISM certification.