Answer
$\forall x[\neg \exists y \exists z \exists w((y \neq z) \wedge(z \neq w) \wedge(y \neq w) \wedge G(y, x) \wedge G(z, x) \wedge G(w, x))]$
Work Step by Step
let us assume that
G(x,y) = “$x$ is grandmother of $y$”
We can rewrite the statement “No one has more than three grandmothers” As, for every person $x$, there does not exist, three people, $y, z$ and $w$ such that the three people are different and such that the three people are each a grandmother of $x$.
Using the above interpretations, we can then rewrite the statement as a mathematical expression:
$\forall x[\neg \exists y \exists z \exists w((y \neq z) \wedge(z \neq w) \wedge(y \neq w) \wedge G(y, x) \wedge G(z, x) \wedge G(w, x))]$
