As executor, you not only have the right, but also the responsibility, to safeguard the property of the estate. You can and should change the locks. You might also hire someone to stay and watch over the property. You will have difficulty insuring the home, if it is vacant, because the insurance company will have some of the same concerns that you do.
You will also want to make a careful inventory of the items that are there, so that you have some documentation of that. This may help if someone later shows up with an item that used to be in the house.
If the Will DOES have a list of items that should go to certain people, I would make every effort to get those items to the beneficiaries, as soon as possible. Those items would not be part of any auction, anyway.
There are a number of different ways to deal with the items not specifically mentioned in the Will. Some people will have a private sale or auction to give the family members a first chance at items that they want. If there are items that have no real value but may have sentimental value, you can always ask if anyone cares who gets what.
You are in charge and you are potentially liable, so do not be afraid to put your foot down on this.
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I would like to put an exclamation point on Mr. Frederick's excellent answer.
As an Executor, you have rights, duties and liabilities. You have a duty to protect the assets, the right to do whatever is necessary to protect the assets, and liability to the other inheritors and to creditors if you fail to do so.
Get the locks changed, notify the local police of your concerns, take photos of everything and take an inventory as soon as possible. Have your attorney send a letter to all the siblings explaining your obligations as executor, and that these steps are being taken at his or her instruction. It is okay to play "good cop, bad cop" with lawyer. There is nothing wrong with working out a scenario with the lawyer where you say "I wasn't sure these steps were really necessary, but the lawyer insisted."
Also, if there are investments and securities, I would strongly consider turning everything to cash in order to protect the value from downward stock market movement during the administration. The stock market is way up this year. If you have non-trustworthy siblings and the market took a tumble, you could find yourself the target of claims for violation of your fiduciary duty to protect the inheritances.
If you are asking this question here on AVVO rather than of your lawyer, it suggests you have not yet hired a lawyer to assist you with the administration of the estate and the discharge of your duties as Executor. Our main office is in Columbus, but we handle cases in all the contiguous counties so if you are looking for an attorney to assist you, we would be pleased to help.