My elderly father (80M) lives back home in a third world country by himself and he has dementia and other health issues.

He lives in his house and there are 3 caregivers working in shifts as he can’t be left alone. We also have a housemaid who cooks and cleans.

I (43M) have two sisters (47F and 42F) and we all live in different countries and have been paying for my father’s expenses equally.

Our family is dysfunctional and my older sister is very controlling and has been threatening for two years to stop paying her share due to a random fake reason each time. A year ago, she stopped talking to me and blocked me on WhatsApp because we had a disagreement on how to manage my father’s care.

I’ve been doing all the leg work in terms of remotely managing his day-to-day life, the house, doctor appointments, hospital admissions, calling him every day, etc I also visit him every couple of months and work online from there.

Recently my younger sister told me that my older sister doesn’t want to pay anymore because “her situation changed” and that me and her (my younger sister) should split payments in half going forward.

They both make more money than I do as I live in Europe where salaries are very low compared to the US and Dubai, where my sisters live.

I think they're trying to rip me off as my older sister will likely pay back my younger sister half of what she pays, so each of them will end up paying 25% of my father’s expenses and I pay 50%.

How can I stop my sisters from using me and convince my older sister to continue paying her share?

TL;DR My older sister wants to stop paying her share of my aging father's care for fake reasons. However, I think that my two sisters are trying to rip me off. How do I convince my older sister to keep on paying her share?