A couple comments/questions:
1) Unless half brother was appointed by the court in a probate proceeding, he is not the executor of anything.
2) Did your wife's father own the property solely in his name? Stepmother can file any quitclaim that she likes, but, unless she legally owned the property, then the quitclaim means nothing.
3) The timing of things: Father dies 2 years ago; that quitclaim; a current(?) request from an attorney for your wife to waive her rights... Was this a case where the stepmother (and half brother) simply forged ahead without regard to the legalities and then had an "Oh bleep" moment?
Your wife probably should check this out with a New Hampshire probate attorney. But it appears to me that they have your wife boxed in. With no will, if I am getting the family relationships right, the surviving spouse would be entitled to the first $100,000 of the estate and 1/2 of the remainder:
561:1 Distribution Upon Intestacy....
I. If the deceased is survived by a spouse, the spouse shall receive:
...
(e) If there are surviving issue of the decedent one or more of whom are not issue of the surviving spouse, the first $100,000, plus 1/2 of the intestate estate.
Therefore, if your wife refuses to sign the waiver, they proceed with probate. The stepmother receives the entire estate under intestacy and can do what she wishes with the property once she owns it. More inconvenient and probably a bit more expensive, but still with the same outcome. Maybe there is some room for negotiation.