Will my dads will be thrown out by a judge because it was not witnessed correctly? Will this make my nieces eligible for inheritance?

My surviving sister & I signed my dads will in front of him and a notary public. We did not know at the time that notary is not required and that we couldn't be witness because we are beneficiaries. My sister, named executor told me her Attorney said the will is not valid because it was not signed correctly and is most likely going to be thrown out by the judge in probate court. My dad purposely left our deceased sister and her two children (our adult nieces) out of the will for personal reasons. The other interesting thing is my sister has been in full support of our nieces getting a 3rd of the share even before my dad passed. She says there is nothing we can do about it that the law is throwing out the will, not her. She has created a serious trust concern with me and I believe she is in her interest only which include my nieces.