What are the minimum leaves to be given to them according to Law?

Since you have decided to remain ananomous, we don't know even which state you are in, I would suggest you read the shop & Establishment act of your state and give the leaves based on that.
If your state has a National & Festival Holidays Act, then read that also.
You can still call the person for work on holidays, but you need to pay overtime and if that day is a weekly off, he needs to be given compensatory off in addition to overtime.
From India, Mumbai
From Vietnam, Bac Giang
From Vietnam, Bac Giang