Need guidance on how to get the property registered.

My Grandfather purchased a property in 1992 on power of attorney in Delhi, the person who sold the property has died, my grandfather also died in 2006. My Father has a GPA of that property issued by the owner of the plot, the property is free hold and the mutation has been done long back, all property tax has been paid till date, my grandfather have 4 children's out of which two died in last 4 years, one is citizen of some other country, my question is that what I need to do to convert the property on my father name, all of my father siblings are ready to provide NOC if required, the only condition is they need there share in the property once we will sell it, but to sell I need to convert the property on someone name in my family, how can I do that? Please suggest.