Who is supposed to take care of $ issues?

Parents ages 85 & 88. Dad is physically impaired with arthritis. Mom has mild to severe dementia. I'm estimating their total liquid assets are around $400K. Their will was prepared naming a grandchild (of which is my sister's son and my nephew) as POA. Will states all assets will be divided equally. Within the past year both parents health has declined significantly. Both parents have fallen as well as some other incidents. He (POA) and my sister insist they need to be in an assisted living community. My parents are adamant about leaving their home. To force them to leave, my nephew and sister will not assist them in any way. I will not be part of this. Without assistance they will suffer. My dad asked me to take on full responsibility. My dad said he will tell the POA that my salary will be $750 weekly. The POA said he cannot and will not do this. Due to the wording in the original documents my parents are confused how he got all of this authority. Please Help!