What steps do I need to take to dispute a handwritten will that was signed by an 86-yr-old, end-stage cancer patient with brain mats?

They were recently discharged with fluid on the brain. I am/was the caregiver for both of my maternal grandparents. My grandma recently passed away from end stage kidney cancer with brain mats. She was hospitalized with fluid on her brain and swelling in January of this year. She was also suffering from severe personality changes, including, depression, extreme irritation, paranoia, delusions, memory loss, headaches, as well as what I categorize as “being a completely different person." One instance of that would be accusing my grandpa of carrying on an affair with someone from church. Anyone who knows my grandparents knows she would never say or think such a thing as they have been happily married for 40 years. Two years prior to her death my grandparents took me to a lawyer and made me their full durable POA, as well as their full medical proxy. At that time both grandparents updated their wills. Grandma made me the executor on her will and named me, and her two sons each 1/3 of her estate. She did not want to include her daughter (my mother) because my mom had been named the only child out of the three children that my grandma shared with her first husband to receive a pretty substantial inheritance when my grandpa (from first marriage) passed. She told me it was only fair that the boys weren’t included in their dad’s will that my mom be left out of hers. Not necessarily left out, but she felt mom was already set. I will mention now that mom and grandma have always had a rocky relationship. My grandma told me, "Please never put your mother in charge of my healthcare or my business.” This context relating to my mom possibly pulling the plug on my dad two years earlier. She was leaving me one third, because I was the one taking care of them from day one. She and my grandpa would call all day, every day sometimes. Grandpa still does and its ok, I’m happy to do this for them as they raised me from the age of 9. My Uncle M. is 66 and bipolar and has numerous other issues and not the highest I.Q. Not being insensitive, just saying. Grandma has basically supported him his whole life up until she died. She left the remaining third to her other son. After making this will she later decided it would just be me and the uncle she took care of because she had given the other uncle 70 acres of land and a house. She actually sold it to him, he was to pay $1000 a month and only ended up making one payment. The courthouse has the property signed over as a gift, however change was never updated in the will. Fast forward to March of this year. Grandma was getting worse. Episodes were pretty far out. I was doing 80 percent of her care as well as my grandpa and my mom did help with dropping off food, etc. In April I started leaving to go to Texas to see my husband. He is currently there working, so I went to do his laundry and grocery shopping, etc. All with a four year old in tow. My mother would help check on them while I was away. My husband worked their five months. I was there a total of two and a half weeks (spread out over the five months). My husband's motor went out in his truck so I had to drive another vehicle over until he got it fixed. I asked my mom to check in on my grandparents and to have her pick up my niece who I also watched after school, she agreed. While I was gone she took my grandma to her personal lawyer (who she used for my dad's succession as well as his parent's succession) and my grandma wrote a handwritten will the states, I leave my daughter, her name, as executor of my will and all of my property. Dated and signed. The lawyer had my grandpa, my uncle, my mom’s boyfriend and one other person. I don’t think grandma should have signed that as her mental competence was questionable. She was matriarch, so sometimes it was just easier to go along with it. She died three weeks later. What can I do about proving she should not have been signing documents? My grandpa got his money back from the shared lawyer and is looking for new council. I have gotten the medical records. Now what?