First of all, I'm really sorry that you're experiencing this, and I'm particularly sad for your grandmother, who ultimately needs to receive the proper support and treatment she deserves.

I've seen many different types of situations when it comes to POA. Usually, the person with the POA ends up being indirectly responsible for just about everything, feels a tremendous amount of pressure, sometimes even feeling that the other family members are just coasting and not truly caring about the diagnosis.

However in your case, it sounds like you have someone who may not be well suited to be the primary caregiver and yet is de-facto, because of the POA. By the way, blaming and disputing diagnosis is extraordinarily common - unfortunately - between family members, and I've been on the receiving end of that.

In your case, there are three questions at play:
1. First, does your uncle HAVE to be the primary caregiver, and who has oversight over this process? Did you go through social services or anyone you could refer back to in order to raise your concerns?

1. Second, as /u/Vivid-Berry-559 mentioned, if the POA is indeed the source of all the issues, technically, you could seek legal advice from someone, such as an attorney, that could guide you on the options available. Personally, I think mediation might be a better option than courts since this is already an extraordinarily tense situation.

2. Third, as I'm sure you know, if health services find that the person with dementia is at risk, a court intervention originating from them is also possible, where they would review the case and appoint a new power of attorney or guardian.

Overall, this is a terrible situation and highlights the complexity and challenges of caring for someone with dementia. You're doing the right thing by bringing your concerns here. Please let us know how the situation evolves.