Can a power of attorney hold money that is supposed to be splitted?

My boyfriend and I are going to be moving out of his parents home,they will be put into a home.Their Alzheimer's and dementia has gone to far.His sis, the POA is going to sell the estate to pay for their board and care home,and what is left,is supposed to be divided between herself and my BF.Things are already getting ugly,and they have not even ped, she is threatening to take him off the will if we dont stay. Can she do that?