Each of $P, Q, R, S, W, X, Y$and $Z$ has been married at most once . $X$ and $Y$ are married and have two children $P$ and $Q. Z$ is the grandfather of the daughter $S$ of $P$. Further , $Z$ and $Z$ are married and are parents of $R$. Which one of the following must necessarily be FALSE?
- $X$ is the mother-in-law of $R$
- $P$ and $R$ are not married to each other
- $P$ is a son of $X$ and $Y$
- $Q$ cannot be married to $R$