Irrevocable power of attorney principal dead

Power of attorney dies if principal is dead in case of gpa but what about irrevocable one written by an educated person who has no idea of law.

What will be Legal aspects of unregistered/registered non-revocable(irrecoverable) power of attorney.

Is hand written unregistered power of attorney on white sheet is valid ? Or it needs to be on stamp paper and must be registered ?

My uncle says he holds non revocable power of attorney, he says my grandmother gave all the property to him to sell. The problem is that before her death, she wanted to register some property to her grandchildren in 2009 but she died suddenly.Hence grandchildren did not get the property which she wanted to register.

He has power of attorney which is written in 1997, which was given to sell the property as told by him but was not sold.

What to do in this case ? There is a state of confusion because of this .
Second problem is that he is not willing to give the copy of power attorney.
Because of this we are neither able to use the land nor able to sell it .

Is this power of attorney valid? Even if it is valid and written to sell the land. Does it gave total right on the money as my grandmother died. What are the implications of this power of attorney.
I would like to know if her other children and her grandchildren has any right left on property or not? Do they have right on the if property is sold?

What if power of attorney holder says it is not his property and now ready to sell it and is going to build building over there citing that by law he he is own of the land as power of attorney will be termed as will in this case ?

How far my uncle's analogy is correct and legaly sound ?