If $R$ is described as follows $R = \{ (p, q) \in P\times P | \mbox{ The person } p \mbox{ is a parent of the person } q\}$, and $P$ is the set of people.
I describe $S$ as the follows $S = \{(p, q) \in P\times P | p \mbox{ is ancestor of } q\}$
Is this enough?
You are correct! You should probably justify your claim, though, perhaps by showing that the relation $S$ (as you have defined it) contains and is contained by the transitive closure of $R.$