$M$ and $N$ had four children $P$, $Q$, $R$ and $S$. Of them, only $P$ and $R$ were married. They had children $X$ and $Y$ respectively. If $Y$ is a legitimate child of $W$, which of the following statements is necessarily FALSE?

1. $M$ is the grandmother of $Y$
2. $R$ is the father of $Y$
3. $W$ is the wife of $R$
4. $W$ is the wife of $P$