Questions about real estate and estate administration are best asked of an attorney face to face. I suggest that you contact the Dauphin County Bar Association’s lawyer referral service at (717) 232-7536. You will be referred to an attorney who practices real estate or estate administration law for an initial appointment to analyze your situation. Many attorneys charge a reduced fee for the initial interview.
Some of the factors to be considered in your situation are whether the 3 siblings inherited the property by a will or through intestacy (no will), whether the property was left to the 3 siblings as joint tenants or as tenants in common, whether the will allows one person to sell on behalf of the 3 siblings, whether the property was a specific bequest or part of the residual estate (if there was a will), and whether the person who is signing is the executor or administrator of the estate.
As with any online reply, this response is limited by the few facts provided and the specific question asked. There are most probably additional facts that could change this reply. This response is not intended to be legal advice, as additional information would be required to provide definitive legal advice. This response is not intended to, and does not create, an attorney-client relationship.