If my natural mother died in Texas without a will and she is married, are my brother and I entitled to part of the estate or does the estate revert to my step-father solely.

The proceeds of her estate will go to your step dad, unless you can find a will saying otherwise.

Hello kz:

It depends on how title was held in the real property. I think you're an heir, though, and have a claim on the personal property. If it's being denied, then you may need a lawyer.

excon

This site explains the law of succession
http://www.professorbeyer.com/Articles/Intestacy_Texas_Basics.htm

Based on what it says you do have a claim against the estate.