I'm not a Michigan attorney, but I suspect the POA did not survive the death of the principal.
His aunts may have additional problems because in some states concealing a will of a decendent with intent to thwart its probate is a crime. Definitely get a Michigan attorney and Good Luck!
She definitley concealed the will. We're not gong to try and charge her with a crime, unless she continues to obstruct. It's great leverage.