Your step children will not automatically be treated as your "children" or "descendants" in your will. If that is what you want, then they must be specifically named as such.

It is important to avoid ambiguous phrasing in a will.  For instance, let's assume that you DO want your step children to inherit as if they were your natural-born or adopted children.   If so, you should specifically name them, stating that they are your step children, but that you want them to be treated equally with  your other children. (or that you have no other children but, for purposes of this Will consider your step children as your own children and descendants).  In this case, you must be sure that the proper language is used throughout the entire will, which may require writing "custom" definitions of "children" and "descendants" at various locations of the will. 

Another option is to name your step children as beneficiaries for specific items, or a specific sum or percentage of money.

And, since your step children are not legally considered to be the same as your children (unless you have legally adopted them), you generally won't need any language to "disinherit" them if you don't want them to inherit from you.  Again, you must be sure that your will is not ambiguous. If you anticipate a contested probate contest among your family after you are gone it may be advisable to be as specific as possible, even if not legally required.

Remember, your will is the document that will be used to pass YOUR share of the estate.  In Texas, your spouse must have his or her own will. Your documents do not need to be mirror images of each other. You are each allowed to have your own beneficiaries, and to leave instructions that dispose of your portion of the estate in any lawful manner that you see fit.