No, that is not true. Did your wife have a Will? Even if she didn't you were married so, her estate should go to you and your children (if you have any).
Your wife's twin is worrying you unnecessarily. Since you were the spouse, you are declared first of kin and will inherit her estate unless there was a will.
Turn the tables on your wife's twin if she wants to play this game. Remind her that she shares the DNA of you wife and may end up with uterine cancer as well.
Bull shit! No, she is not entitled to anything because she was your wife's twin. This is about the most ridiculous thing I have ever heard. Sounds as though she may be alittle unstable. Don't let this crap bother you, she is full of it. . . . . .