Will valid or not

Hello, I have some questions in regard to my grandfathers property, please help. 1. My grandfather had only one son that is my father, and grand mother passed away before grandfather. Now, grandfather made a will of his property to a lady stating her as his wife in the will. The lady has four children from her previous marriage and had no children with my grandfather. The lady died and her four children has captured my grandfathers property currently. Questions are: 1. Will was made in the name of the lady, the lady died but she didn't take probate of the will. The will is not registered or lady didn't take probate of the will from the court. Is the will valid? Is she the valid owner of the property without the probate of the will? 2. If she is the valid owner of the will without the probate obtained, is the property she inherited from the will automatically transferable to her four children although they are not the blood lines of my grandfather? 3. If she is not the valid owner of the property because the probate is not done when she was alive, does the property go back to the real bloodline of my grandfather, that is my father? 4. As she is dead 15 years back, can her own children from previous marriage go to the court now for probate or to validate the will now after 15 years, so that they can get the property? 5. If the will is invalid without the probate and she is dead long back to validate it now, does it mean that she was never the owner of the property? So the question of her four children from previous marriage getting the property now after her doesn't arise at all?