I suggest you take a look at the will. Your mother may have changed it, or your stepfather may not understand the situation. Whoever presented the will for allowance should have provided notice to you. If anything has been done to probate this estate, and I hope by now something has been done, you may have missed your opportuntiy to object.
Please note: The above is for general information purposes only. It is not intended to establish and does not establish any attorney-client relationship.
I'm sorry for your loss. It is unclear from the facts presented as to whether your mother's Will has been admitted to probate. Thus, I'll have to deal with two separate scenarios.
Your best chance lies with a fact pattern in which the Will has not been admitted to probate. In that case, depending on the terms of the Will, you may be able to argue that the Court should appoint an independent fiduciary due to the conflict in your family.
Unfortunately, if the Will has been admitted to probate, you will have a much higher burden. That is, once your step-father is appointed as Executor, you will have to show that your step-father has breached a fiduciary duty to have him removed from that position.
In any event, you and your siblings should hire an experienced probate attorney as soon as possible to advise you of your rights and to protect your interests in your mother's estate. Good luck to you.
This information is presented as a public service. It should not be construed to be formal legal advice nor considered to be the formation of a lawyer/client relationship.
As long as the probate case is open, you always have time to seek removal of an executor (now called Personal Representative.) As mentioned by others, it is really a question of continued qualification to act. initially the Court found that the person now acting was in fact qualified. The Will governs who is appointed unless there is finding that the named person is unable to act. The Will tells you who your mother wished to act for her. if there was no Will, then, as mentioned, you will have to show that something has happened since the date of the initial appointment of the Personal Representative what would support a court Order removing that person at this time.
This comment does not create an attorney-client relationship. The law and its application by the courts is constantly evolving and changing. This discussion is not to be taken as a definitive guide, and should not be relied upon to determine all fact situations. Each set of facts must be examined separately with the current case and statutory law analyzed and applied accordingly.