Dear Jayasimha H.,
Your question on declaration by contractor, I said no such declaration will work or no such declaration will help you.
The contractor is legally bound to make the proper compliance whether he gives you a declaration or not. However, if he fails to make proper compliance, you being PE, responsible and liable jointly and severally even you have any kind of declaration by him. And therefore I said no such declaration will work.
However, you can take undertaking and indemnity from the contractor by which the contractor undertakes to make proper compliance of applicable laws from time to time and indemnifies you in case of any damages / loss to you by his any default. Labour Law or any Law as such is very vast subject. One can miss-out some thing and because of that there is some damage / loss to you, you can always have indemnity as suggested by me.
Before insisting indemnity by contractor, you must know what are the laws applicable to you and what are your responsibilities and liabilities under the applicable laws. You need to hire the service of a person like me who can help you in all regards. You can get from me not only legal advise but also any kind of service such as providing manpower, security guards etc. with proper compliance. But you have to pay my cost to me. You can go through my both the websites as given below my name.