My father passed away six years ago, we did not transfer the property to brothers and sisters. Now we are cosidering selling the house, we 2 brothers are in the US and citizens of US and rest are in India. What are the India tax obligations for we 2 citizens of US?

A US citizen and resident must report worldwide income. When you sell the house, you must report the profit from your share of house. For US tax purpose, the cost basis of the house is the fair market value at the date of death of your father.
If you paid taxes in India, you will file Form 1116 to claim foreign tax credit. Your U.S. Tax Return: U.S. Citizen or Resident with Foreign Income (http://taxipay.blogspot.com/2008/03/us-citizen-or-resident-with-foreign.html)
Did you or your family live in the house for two years in last five years?