Any can file, but all three should be appointed unless they waive their right to serve. There is no priority among the three, by age or otherwise, unless the will gives such a priority. Equal executors means what is says: it takes all three.
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If the will names the three siblings as executors, they will have equal power. Whether they must act jointly or may act separately may be specified in the will. Under the Texas Estates Code, any one of the executors can act for all of them if the will does not specify how they shall act. To transfer title to real estate, all three must sign. The relative age of each executor does not determine relative authority.
It is generally not possible to address all contingencies in a brief answer. My answer is based on the facts as provided and on general legal principles that may not apply to your specific situation. As a result, my answer is necessarily preliminary and should not be relied on without consulting an attorney who can fully evaluate your circumstances. Nothing in this communication creates an attorney-client relationship.
You really should hire an attorney to help with this, especially if there are multiple executors. Any of you can file to probate the will.
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