What do you mean by interns? Are they students who have to do internship as part of their curriculum? Or are they trainees? Or Apprentices?
Interns are those who are undergoing some curse of study who have to do internship for a specified period as per the curriculum. After completion of the internship, they will go back to their colleges to complete their course. If this is the arrangement, you pay stipend without deducting and contributing to any PF or ESI.
If you appoint trainees or any person as trainee you should pay all statutory contributions as are applicable to regular employees.
You can appoint apprentices following the provisions of Apprentice Act. Such apprentices are appointed through Related Instruction Centre. If you go for optional trades, you can engage apprentices by registering in the portal of apprentices. Please go through the guidelines of national apprentice programs. You need not pay any PF or ESI. The number of such apprentices will depend upon the regular employees. There are some conditions of appointing apprentices, like you cannot engage them during night, you cannot ask them to do overtime etc. That means you cannot run your establishment with trainees only!