My father recently passed away. He was 89 years old and

My father recently passed away. He was 89 years old and lived in his own home. His newly appointed Executor to his Will (his niece-in-law who is a nurse) found his body.
He was in a wheelchair, had an ostomy and was hooked up to oxygen, and was deprived of same numerous times in the past 2 years.
He signed his Last Will on March 5th, 2021, three days prior to being rushed to hospital (March 8th, 2021) resulting in emergency surgery. He was released from the hospital on March 17th, 2021 and his new Executor (niece-in law) brought him home. He died on April 8th, 2021. His Executor left a voice message on March 17th stating that she had spoken to his doctor and he was being released. She left another voicemail on April 18th stating she never spoke to a doctor during my fathers stay in the hospital and didn’t know what his surgery was for! The hospital would not give me any information as according to the new executor she had been chosen to handle his medical affairs including communication’s at the hospital.
Interestingly, two days prior to the signing of my father’s new Will my friend and I visited him (March 3rd, 2021). My father was laying down on the sofa and was not able to sit up and repeatedly told us he was in pain and dying.
After leaving my fathers house I received a text message from his niece-in- law asking that I not come back the next day and to let her know in advance when I was planning on visiting.
At no time was I told by my father or the nurse that he was planning on changing his Will.
Prior to Covid my father stated numerous times that he didn’t like his niece-in-law or her daughter.
He died one month after the nurse cemented herself into his life.
It is my belief he was pressured to change the content of his Will, his Executor, Trustee, and Power of Attorney to his niece-in-law who acted as his nurse, banker and personal secretary destroying documents in his office prior to the signing of his new Will.
I have voice recordings from his new Executor proving that she is not truthful and certainly can’t be trusted.
I don’t trust anything the Executor says. I would appreciate any advice you might have for me going forward.