You and your siblings should hire an estate lawyer and object to the girlfriend being appointed as administrator.  This is the first step.I do not know of a single state that would allow a girlfriend to inherit in the absence of a will.  Florida does not allow it.  In Florida, family members have preference to serve as administrator (personal representative in Florida) in the absence of a will, not a girlfriend.There will be other steps.  Appointing an administrator is just the first step.  If I were you, I would start looking for the lawyer who may have prepared your father's will.  That lawyer should at least have a copy, and a copy can be admitted to probate under some circumstances.  The will could be in a safe deposit box.The girlfriend will have to prove she is your father's spouse in order to be administrator or inherit.  I don't know what state you live in, but most states no longer recognize common law marriage. I do not recommend that you and your siblings attempt to deal with this on your own.  You should consult a lawyer.