Canteen Lunch Policy and Deductions
It is not compulsory for every employee to have lunch in the canteen. It is not legal to charge workers who are not availing of the lunch facility. You can charge for those who are casually absent (those who eat sometimes but not all times) because the food needs to be made for them, but you cannot force anyone to eat your canteen food or force them to pay (by way of a deduction).
In fact, it would probably make more sense then to consider the deduction for the canteen as part of CTC but not as part of the salary, meaning it is a welfare payment and not asking for a contribution from the workers. But that is an internal management decision and probably connected with the agreement you have with your canteen contractor.
Canteen Committee Members' Participation
There is no rule to say that canteen committee members have to eat in the canteen. But it is a matter of internal management. If they are not eating in the canteen, then it is possible they are not really interested or concerned about the canteen and therefore they should not be in the committee. But there is nothing in the law to support or prevent this; therefore, it is an internal decision.