Usually after the death of original owner without Will the property will devolve upon his children. Thus the grandchildren have no share in the said property. But for safety reasons you may take signatures of grandchildrens and five children of original owner on the sale deed. The law in respect of Ancestral Property is as follows:
What does the grandparent's property law in India state? Does the grandson own the right to the property?
All property's owned by a Hindu person devolves onto his class one legal heir's.
Now to the specific scenario's in ur example (for sake of convenience I'm presuming ur ur grandfather has only one legal heir)
Senario1: The property is self acquired by your Grandfather, in such case upon his demise interstate (without a will) the property would devolve upon ur Father and not you. In case your farther passes away before your grandfather then it such case it would be devolve upon you, your mother and ur siblings equally.
Scenario 2: the property in question is self acquired by ur grandfather father ( ur great grand farther) - would devolve same as scenario 1.
Scenario 3: the property in question is self acquired by ur grandfather grand father ( ur great great grand farther) - would devolve same as scenario 1.
Scenario 4: the property in question is self acquired by ur grandfathers great grand father ( ur great great great grand farther) - then in such a case you would be entitled to the property by birth as it becomes ur ancestral property.
To give you more clarity on the concept of Ancestral Property's : any property which passes undivided down 4 generations of male lineage is called ancestral property. The right to such property acures at birth unlike other laws of inheritance where right arises upon the death of the the owner.
Hope this brings some clarity to your question and your sense of entitlements.