IF he becomes the executor or administrator of the estate, THEN he can change the locks IF doing so is in the best interest of the heirs and beneficiaries: the executor or other court-appointed administrator *must* act in the interest of those who will inherit, whether under a will or under intestate success (who gets what, if there is no will). The executor or administrator cannot act in his own interest, and one beneficiary taking advantage for himself is also illegal; the way to respond to this is to bring a legal action in chancery, probate, or surrogate's court (call the court clerk; they can direct you to the approopriate court to file in, in your county) seeking a court order laying out how the property must be dealt with.