land demarcation

Are you paying land revenue separately?     Are there separate revenue records on your separate names?

You can challenge the sale of the properties of the other two.

obviously we have separate revenue documents and are paying land revenue separately

Your difficulty in having demarcation was not explained and it is safe for you also.  They can not demand a separate road for them after 30 years with out any such easement rights being enjoyed for the last 30 years.

The boundary of agricultural land of one of my brothers meets with his in laws land and they have taken some land (shifted the boundary) from it. So after demarcation my brother can have at least 1000 square feet less than me. He is hand in glove with his in laws and asking this 1000 square feet from me instead of his in laws. More over I cannot ask the government to demarcate the land of his in laws as that is not our property land. That is why I'm against demarcation. Also he is asking for a road (8 feet wide path) to his land through the center of our land.
At another place he had a piece of land by the road side and my land is behind his land. He sold his land without giving me a similar road. Now he claims that I should give him a road at another place where I have taken land by the road side.
Kindly tell me what action the law can take and what I should in this matter.

The best course is to enter into a settlement deed incorpoarting all the aspects. Mere payment of land revenue will not confer title to property. However, adverse possession/occupation could be the decisive aspect.