joint property issue

My grandfather has 3 sons; my day is an elder son. A property was registered as a joint property at my father�s age 25 (on my father�s name and my grad father�s name). Total joint property was 4 acers of land which was registered one day. On the other day, another 1 acre land was registered on my grandfather�s name. Now my grandfather has expired. As per this situation 1. What is my father�s share Please explain this? One of my friends told me that my father share would be 3 acres (50% of joint property and equal share among 3 on the rest of 3 acers of land). Is this correct or not. If not some please help us to understand the laws. or All there has to share 5 acers of land equaly.