Grandmother and special needs (SN) aunt being taken advantage of by aunts. Advice?

Hi everyone. I'm at a loss as to how I should handle this situation.

My grandmother's health plummeted about a year back, and we thought she wouldn't make it. During this time I was stuck in a foreign country with no way of coming home because of Covid. A cousin of my grandmother's and her daughters offered to have her and my SN aunt to come live with them and my grandmother agreed. We all thought this would be a happy reunion, because both her and my SN aunt were cooped up all by themselves in their house and didn't have anyone to come to the rescue if something happened.

Fast forward about 6 months after she moved in with them. She's overcome what had gotten her sick initially and I manage to come back home to Nicaragua. Everything seems fine until my grandmother's nurse starts spilling the beans and tells me that when my grandmother was very close to passing away, the people she is staying with made her sign a power of attorney while barely conscious. My grandmother's savings have all gone out the window and she is being treated poorly in their home. I have been trying to get my grandmother and SN aunt to come move in with me since I found out about all of this, but she has been impossible to convince. I don't know that I would be able to support an additional 2 mouths in my home, as we're already pretty tight month after month, but I'm sure I could figure it out.

Here's the kicker. My cousins, who all live in the states, and I got into a huge argument with the people grandma is staying with because now they are demanding we send 2.5k dollars for medical care for my SN aunt without offering any receipts. The most we have gotten is an excel sheet they whipped up with random numbers. They have been pressuring us to come up with the money by saying they won't initiate treatment until they have the full amount and that my aunts health is declining with each passing day. They also added that if they don't receive the entirety of the money, they absolve themselves from all responsibility if anything unexpected happens to her. (I might be wrong, but isn't this extortion?)

They claim the medical costs my grandmother and aunt have required over the past year exceeds 30.000 dollars (which is absurd in a country like Nicaragua. We are a third world country, after all), but refuse to show proof of purchases, receipts, doctor prescriptions, etc. I will be going this weekend to get a bag of receipts they say they have, but I have a strong feeling things won't add up.

I guess I'm just looking for advice on how to deal with this, as I fear that if we make them angrier with the constant back and forth, they will become even more hostile towards my grandmother and my aunt. My grandmother has already requested us to stop, as we are "making things worse for her."