In conclusion, all of the options listed (lack of consideration, absence of grantor's signature, omission of legal description, failure to notarize the document) could potentially cause a grant deed to be invalid at its inception.
The deed becomes voidable when there is proof that, without the undue influence of another, the grantor would not have executed the deed as written. Stewart v. Miller, 271 S.W. 311 (Tex. Civ.
Texas law states a clear distinction between forged deeds and fraudulent deeds. Forged deeds are declared as void, passes no title, and are treated as null. A fraudulent deed is voidable and will be passable until set aside or struck down by the Court.
You have two options: (1) sign and record a revocation or (2) record another TOD deed, leaving the property to someone else. You cannot use your will to revoke or override a TOD deed.
The short answer is yes. Anyone can sell your property without your consent.
Specifically, if the deed is void, it does not pass title and cannot be enforced even if recorded and even if title is later acquired by a bona fide purchaser. (Gibson v. Westoby (1953) 115 Cal. App. 2d 273.)
Unfortunately for you and your other siblings, the Will generally does not override the Deed. Rather, the general rule is that the Deed controls.
The Transfer on Death Deed beneficiary takes subject to all mortgages, liens, and claims. If you die with outstanding debts, the property could be tied up in probate for up to two years, until the period for creditors to make claims against the estate expires. A Transfer on Death Deed trumps a will.
If you have made a will or previous TOD deed that leaves the property to someone, your new TOD deed will override it. Your rights. You keep complete ownership of, and control over, the real estate while you're alive.