Challenging a registered Will on basis of a cancellation of a previous settlement deed

One of an elder sister of my mother who is unmarried demised some weeks before. One week before her demise she registered her Will on her property, putting me and my sister as the equal and only heirs of her property. Now her brother’s sons are indenting to challenge the will enforcing the undue influence on us.

There was an older registered will of her stating the same matter in it also. One year before the old lady registered a deed of settlement on the name of us (me & my sister) for the purpose of a construction of a building. But we could not start construction procedure because of a financial crisis. After 4 months she cancelled the settlement deed to make the property on her name again. We exchanged our fear about the validity of the previous Will after the cancellation. Then she also agreed to make a new Will and then it registered.

But after her demise the above said brother’s sons argued that cancellation of the deed itself shows her unwillingness to make a Will on our name. They have taken this as their basic ground for their contest of undue influence.

I want to know, will this stand on the court? Will this affect the validity of the Will?