My stepbrother & his wife was given POA over my father, this was done right before my stepmother died. Can I contest the POA?

My stepmother had my father go to an attorney 2 weeks before she died and had the trust changed and gave her son & his wife POA over my father. I know my father does not understand what a POA is, does or can or can't do. When I ask him why her son and not any of his children were given the POA, he says that the law made the decision and that is how it was. He also refuses to let anyone on his side of the family see the trust or the POA papers, because the law said we couldn't have access to them. I do know that none of us on his side inherited a thing from her passing, but I do know that the trust now states everything will be divided between her son, his wife, their 2 children, me and my brother. I have asked him what happened to her 401k plan, her savings, life insurance policy and he has no idea where it all went. My stepmother has manipulated my father for years into thinking one thing while she was doing another. She uses his lack of knowledge, his inability to hear, and his health to get what she wants while telling him either nothing or making it sound completely different than what is really going on. She has managed to isolate him from his family, which he doesn't realize, drained his savings, made him pay every bill in the house, even though she was still working making very good money and he was living on $660 SS and a small pension. It is all about her son and his family. He was always having to stop everything he was doing and cater to his stepchildren and her son's wife. Yet he has done nothing for my daughter and grandchildren. We have never been invited to a Christmas, Thanksgiving, or even to celebrate his birthday. Once he lost the ability to drive, we have never received birthday cards, Christmas cards, or anything. When I finally confronted her about making him pay all the bills, which was quite a showdown, she finally started paying the electric, gas and cable. My father owned the house way before she and him were married, and before this last trust change, it had stated that she had 6 months to either move or pay me for the house. I really need to find out how I can contest the POA and gain access to the trust. We live in Kansas, and even though I am a beneficiary of the trust, and have a right to see it, he will not allow it. I truly believe that he was manipulated into having everything in the trust and POA changed to benefit her side of the family and leaving his side with very little. I really believe he has no understanding of what took place and how it will affect everyone.