1: First of all check whether there is any statutory provision regarding festival holidays in your state, (like The Kerala National and Festival Holidays Act 1958) or else when the holiday list of the succeeding year is decided, pl reckon the festival holidays of that year and avoid all such holidays. But National Holidays viz., Republic Day, Independence Day & Gandhi Jayanti are to be invariably holidays and cannot be exchanged. Where such holidays occur on the same day and where there is no statutory provision, there are different practices like allowing a separate holiday on another festival day, allowing any one day as optional holiday/cl though such a day is not a festival day, adding one more cl , extra compensation for the day lapsed etc being followed by the establishments.
2: Section 52 of the Factories Act 1948 holds the answer. In a nutshell it can be said that the weekly holiday can be shifted to any preceding or succeeding three days by issuing notice and such shifting can be done upto two months with the approval of Factory Inspector under Section 65 of the Act.