Since it is a property, you are unnecessarily trying to find some justification to stake a claim on the second property. You will come to know after reading the following answer that your expectation has no basis and in fact your father/you have no claim over the 50% of the second property which your grandmother WILLed to her brother-in-law's 4 sons.
Now, you are concerned only with the Second property. Therefore I am confining my reply to the second property alone.
As per you, your grandmother along with your father got the property in her name after the death of your grandfather. In fact, after the death of your grandfather, naturally the property has to go equally to all his legal heirs. In this case, the legal heirs of your grandfather are his widowed wife (i.e. your grandmother) and his son (your father). That means, each will have 50% share in the property left behind by your grandfather.
Now, through the WILL, your grandmother has left 50% to your father, and only the remaining 50% (which actually fell to her share in the inherited property) to her brother-in-law's 4 sons.
When your father has got his rightful 50% share in the property left behind by your grandfather, what more is required.
The 50% which your grandmother WILLed is out of her own 50% share. Therefore, you or your father have no legal claim over the same.