Your grand mother can execute will for property inherited by her through will 

2) will should be attested by 2 witnesses 

Hi

Yes she is fully entitled to create the Will for the property.

She got the ownership of the property via a will so she became the owner and have full right to get a will registered for it.

Only you have to confirm is that both the wills were registered or not.

If not registered then her ownership is not clear and you can challenge the partition in court.

Thanks 

She can execute Will. Under section 63 of the Indian Succession Act, 1925, a Will is required to be attested by two or more witnesses in the presence of the testator.

1. Property received thru a WILL, is classified as "self-acquired" property at the hands of the will beneficiary. Hence in the case instant Grandmother is the absolute title owner of Grand Father's property.

2. Grandmother is absolutely entitled to Sale /Transfer /Gift /Will /Donate /Mortgage /whatever.... to ANYBODY she wishes to in proportions according to her wish.

3. Grandmother's WILL can be challenged on grounds of her mental instability, mental coercion, forgery etc....

Your grandmother became the absolute owner and there had full right  to dispose of the property as per her wish. 

Yes. The property became self acquired if she received the property through a will. Now she can dispose the property as she likes.

The property acquired by your grandmother from her husband through a Will shall become her own and absolute property.

Therefore she can very well transfer the property lying on her name with clear and marketable title to anyone of her choice and in any manner including by testamentary disposition.

Thus there is no illegality in she transferring the property by a Will to the beneficiaries in the manner as described in the Will.

First need to check whether the WILL prepared by grand father is for self owned property or ancestral property.

If it self owned property then both grandparents has rights to prepare a WILL as per their wish otherwise not (Because they can prepare for their shares only if its ancestral property.)

Yes your grand mother can prepare a valid will for the property she receive from the will, she is absolute owner of property and the will made by her for same is valid. 

Yes, your Grand Mother can bequeath the property received by her  in the form of Will.

It has to be witnessed by two witnesses. 

- As per law, your grandfather was having right to transfer his self acquired property to anyone , and hence the property transferred to his wife via WILL was legal . . 

- Further, through the WILL executed by your grandfather , she retained the ownership of the property, and thereby she was also free to transfer the said self acquired property to your father legally. 

- Hence, the WILL executed by your grandmother is valid , and non-changeable. 

It is to be seen whether your grand father Willed his ancestral properties as well to his wife or not.

If the Will of your grandfather contained his ancestral property then your grand mother by that Will doe snot have exclusive right over the said ancestral properties and hence she can transfer those by her Will at the deprivation of your father.

So you father can challenge those Wills and claim his due share by filing a suit for partition but only in respect of the ancestral properties and not self acquired property of your grand father  if included those Wills. 

Yes. She was absolute owner by virtue of Will and bequeath to any one. 

Now dispute can bring on Will only if duly executed by grand father. 

Yes if the same is now her self acquired then she can prepare otherwise she can't

Yes she can definitely write the will for property she have inherited through will of her husband.