Can I somehow legally move into my dad's (95) to care for him against the wishes of the POA?

my sister is the p.o.a. of my 95 year old father , who has dementia.2 years ago she said her & her husband were going to move in & help him since they have a car & more $ than i , i moved out . they never moved in ,so i began moving my stuff back in , he needs one of us there but now she & my mom ( dads ex) harrass me , throw away all my possesions every time i leave the house to go to work .what do i do? they want to hire a stranger to move in but my dad is horryfied at the thought