What can I do about sister that moved in to father's property and sold valuables?

Theoretically, you could open your father's succession, have an administrator appointed, and haul your sister into court to explain where everything went and what she did with the proceeds.  And then, theoretically, the court would order her to pay everything back that she was not entitled to. Realistically, the heirs might spend a lot of money to hire an attorney, and the estate might not be able to collect anything from your sister. Sadly this happens sometimes when the heirs do not open a succession promptly and administer a person's estate under court supervision. Based on your question, it appears that real estate is involved, so the heirs will sooner or later have to deal with property maintenance, payment of taxes and insurance, and a possible eventual sale of the property. And that will likely require formally opening the succession and getting the court involved.