First, go to the county courthouse in the county where Dad died and see if a will was probated. If it was, get a copy of the will and read it to determine what it says. It is not unreasonable to think that, after 27 years of marriage, Dad left everything to his wife. However, we won't know until you see if there is a will. We won't know what rights you have until we know what's in the will. You probably have to take the will to a probate lawyer for advice on what it says and what your rights are.
Second, if there was no will, hire a lawyer and open up probate yourself. In Texas, you will be entitled to a share of the estate if there was no will. Thus, you can open up probate and figure out what happened to the assets.
Third, stop signing things until you know what they say.
If you open up probate, the stepmother will have to produce the will (if there is one).