I am the only sibling. I live in Phx, AZ and they live in Kansas City KS. I didn't know she gave her 2 older children POA until my father passed away after she died. My sister passed away last June 2017 and my father passed away this past February 2018. The POAs have not shared any details of what is to be done and I being the only sibling alive and out of state, what rights do I have to any financials?
As DeeAnna said, POA responsibilities are over when the agent dies.
It is likely that your sister's estate will be inherited by her children and that her children and you may benefit from your father's estate.
In any case, now that you have also lost your father, which I am sorry to hear, it doesn't matter because any power of attorney ended at that point.
Your father died intestate. If you are sure that was the case, look up "intestacy in Kansas" and take your research from there. This link -
https://www.kansaslegalservices.org/node/1092/frequently-asked-questions-about-probate
- may be helpful in explaining the process.
I am sorry that you are not on better terms with your niece and nephew, not even to the extent of being able to pick up the phone and have a business-like conversation with either, but as your father died intestate it is unreasonable to hold them responsible for whatever is happening to his assets. They cannot be his executors, because he had no will; and four months is really not very long when it comes to sorting out the affairs of someone who left no instructions, I'm afraid.
Your nephew is now living in your father's house, is that right? And was he, or was his sister, your father's primary caregiver? Did you have any involvement at all in your father's life?
I do understand the tension and frustration of feeling that you are being kept in the dark, and it can make one very suspicious too. But do try not to let it turn you into the sort of person that on sober reflection you would not want to be.