Did he own half of everything they had or does that just apply to debt?

Texas is a community property state, so once your father married your stepmother, the property and income they acquired became community property. Because your father died without a will, the Texas intestate succession laws apply. They determine who is entitled to what part of your dad's estate. Because he left behind a fairly large amount of property, it is necessary for his estate to go through the legal proceeding known as administration. Please make sure to consult with an attorney who is experienced in this type of law. Your step mother's 401k belongs to her. It will be up to her to determine who should inherit it because from your question it appears she is still alive. If she writes a will, that will determine who is entitled to her 401k and retirement accounts.