Non-family Members Have Poa Over My Grandfather And Had Him Write New Will. Now We Stand To Inherit Nothing. What Can We Do?

TLDR at the end. My grandfather (85 years old) lives in Arizona. My grandmother passed 20 years ago and at the time my grandfather showed us the will which included my mom, aunt, and I as the sole inheritors. My grandfather is not biologically related to my mom; my grandmother got remarried when my mom was 15 and my grandfather never formally adopted my mom or aunt.

A few years ago, my grandfather met a new significant other who he began to live with. He stopped communicating with my mom and I shortly after. Last year that significant other passed away after falling in the home. She was unconscious and bleeding for hours, but my grandfather didn’t call 911 despite being aware of the accident. He clearly wasn’t in his right mind. We now know, the woman’s children then got powers of attorney (healthcare and financial) over my grandfather at that point. They have relayed that they asked my grandfather if he had family to call and he said no, again showing he wasn’t in his right mind. We found all of this out a year after. I found the other family’s grandson on social media and finally got in touch.

We are in touch again with my grandfather who is now in a home and has further reduced mental faculties. We suspect that these individuals who hold the POAs also got my grandfather to create a new will at the time. If my grandfather said he had no family he likely said he had no existing will. The estate will be worth $1 million-$2 million.

We are concerned that they had him create a new will when he wasn’t competent. Now they are being cagey about letting us visit my grandfather’s home. Do we have any legal standing to challenge the will if he did create a new one?

TLDR: (Arizona location) When a significant other of 4 years of my step-grandfather passed, her children got him to sign POAs and likely had him create a new will. At the time he said he had no family and they relayed that he had let his significant other bleed out after a fall without calling 911 (both showing he wasn’t mentally competent). His mental state has further deteriorated. The estate will be worth more than $1 million. Do we have any legal standing when he passes to challenge a new will written under these circumstances?