There are not enough facts here to give any sort of definite answer and there are documents you may not have on hand (such as prior deeds and wills) that will have to be investigated and reviewed before an actual answer can be given. You really need to hire a local lawyer with experience in both real estate law and probate law.
Just guessing from the information you have provided, however, it sounds as if perhaps the real estate was your grandfather's separate property (either owned by him before marriage to your grandmother or received by him as his separate property during the marriage) and that he and your grandmother lived on it until his death, after which she continued to live on it as his widow and as her homestead, and that he died intestate (without a will). You'll need to check with a probate law expert to be sure about this, but I think that would mean that -- upon his death -- legal title to the real estate passed to his children subject to a life estate that your grandmother possessed. So it may be that the legal title belongs (belonged) to his children (presumably one of your parents and his/her siblings, if any), and that's who will need to sign any deed to convey the real property. It also could be that the real property actually was community property owned together by your grandfather and grandmother, in which event -- on his death -- she owned a 1/2 undivided interest in title to the real estate, with the other 1/2 undivided interest in the title went to you parent (and any siblings), the latter being subject to a life estate in your grandmother, in which even the life estate issue only pertains to 1/2 of the title to the real estate.
And, it could be that none of the above is correct because there is a will that disposed of everything even differently, or some other set of presently unknown facts.
As you can see, this is a fairly complicated legal problem that you almost certainly cannot resolve on your own and it certainly cannot be resolved for you on this forum.
You really do need to hire a lawyer to do the proper investigations and research to be able to advise you of how best to resolve the problem.
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Mr. Dalton has provided you with sound advice. Your most prudent course of action would be to contact a local probate attorney to review and investigate the title to the property. Only then will you have the necessary information to make an informed decision on how to move forward.
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There are a lot of facts in your statement. Its just that they are rambling and difficult to understand. You need to take your facts and as many documents (deeds, probate records) to an experienced real estate lawyer to get a meaningful answer. In general, if your grandmother only owned a life estate (which is easily determined by looking at the deed from her to your sister) then she had no interest in land could be inherited by anyone. To "overturn" a life estate it would be necessary to contest the instrument that created it. That would be very difficult to do after all this time.
DISCLAIMER: This is not specific legal advice and does not establish an attorney/client relationship.
The call of the question is, can a life estate be overturned in Texas. Although I've never heard of that happening, I can imagine some facts may compel a judge to do so in some circumstances- but they would have to be far different from or far more involved than what you have describe. I think Mr. Dalton's first hypothetical is an excellent guess. And,Title Conpanies are not perfect. What I think the attorneys here are basically saying is, you may have some easier ways to the fee title than simply worrying about the 'life estate' determination of the title company.