There is no requirement that a will be probated. If there is a need to probate the will now, the fact that the spouse had the will and chose not to probate it is important because generally a will must be probated within four years of death. To avoid that, you can probate the will as a muniment of title after four years if the applicant (you) were not at fault for the will not being probated. You weren't at fault because you weren't the executor and she chose not to probate it. So, you need a lawyer to probate the will, which must be probated in the County where your father resided at the time of his death or the County where the property exists that is at issue now.
It may actually be possible to probate the Will using an Independent Administration even after 4 years because the step mother prevented it from being probated. An experienced probate lawyer will be able to tell you which procedure is available and best suited to the circumstances. That lawyer can also tell you which situation is in your best interest. It may not be in your best interest to have the Will probated. If the Will left your father's estate to your step mother, you and your siblings would actually inherit more if the Will was not probated.
DISCLAIMER: This is not specific legal advice and does not establish an attorney/client relationship.
I agree with the other two responses, but would simply add that, depending on how the assets are titled, probate might not be necessary, or even allowed. If all of the assets were jointly held, they could pass automatically to the spouse. This could bypass probate AND the Will. You need to have someone investigate further to determine how title was (is) held. This is generally easy to determine by checking the public land records. Your situation is complicated by the fact that Texas is a community property state.
I would also point out that your stepmother has not been made executor. There IS no executor unless and until there is a probate estate opened and an executor has been appointed by the court. She has perhaps been "nominated" to be the executor. There is a HUGE difference.
You need a Texas probate attorney to review this with you and determine what, if anything, should be done at this time.
*** LEGAL DISCLAIMER I am licensed to practice law in the State of Michigan and have offices in Wayne and Ingham Counties. My practice is focused in the areas of estate planning and probate administration. I am ethically required to state that the above answer does not create an attorney/client relationship. These responses should be considered general legal education and are intended to provide general information about the question asked. Frequently, the question does not include important facts that, if known, could significantly change the answer. Information provided on this site should not be used as a substitute for competent legal advice from a licensed attorney that practices in your state. The law changes frequently and varies from state to state. If I refer to your state's laws, you should not rely on what I say; I just did a quick Internet search and found something that looked relevant that I hoped you would find helpful. You should verify and confirm any information provided with an attorney licensed in your state.