You've just mentioned the constitution of your establishment and left its type to other's guess. Anyway, since you are in Tamilnadu and the State has a special legislation for the purpose of grant of national and festival holidays to employees of industrial establishments situated in the State, I presume that yours is a factory or shop or establishment or a plantation or any other specially notified establishment like Beedi and Cigar Mfg.
Coming to your queries, section 3 of the TN Industrial Establishments( National and Festival Holidays) Act,1958 stipulates the grant of a holiday of a whole day on the 26th January, the 1st May, the 15th August and the 2nd October and 5 other holidays for such festivals in each calendar year. The 5 Festival Holidays are to be specified by the Inspector in consultation with the employer and the employees of the industrial estt.
You have to bear in mind that these 9 holidays are not connected with the opening of the establishment but only with the grant of holidays to its employees. Simply put, on these 9 days the employees should be (a) allowed holiday or (b) can be required to work with double wages or a compensatory holiday within 3 days either preceding or succeeding the day of holiday. [ sec.5 (2) ]
Requiring the employee to work on such a holiday is the right of the employer subject to service of a notice in this regard to the employee and the Inspector 24 hours prior to the holiday and exhibition of the copy of such notice in the establishment on the holiday.
Similarly, it is the discretion of the employee to choose either of the options of double wages or compensatory holiday.
For further details, better go thru the TNIE(N&FH)Act,1958 and the Rules,1959.