If your company is paying bonus monthly to the contractor then you have to ask to pay the bonus to their employees. It is the total liability of the contractor but you have to ensure becuase you are paying on monthly basis.
For this you can ask for bonus register "C" in which bonus have to be distributed and one thing you can ensure that contractor will distribute the bonus amount in presence of the HR representative of your company.
During full & final settlement before October, Contractor are not settling the Bonus of the workers.Could you kindly confirm under which section as per Payment of Bonus Act/CLRA Act/any other act is it mention that Bonus should be settled during F&F before October or should be settled later and if not the said amount should be deposited with applicable fund. What is the proof of persons receiving of Bonus if he has regisned before October.