Beth, You could make the earrings deliberately different, which will
actually make the stones look more alike. I don't know what style
you work in, but here's an example. If you started with 2 "fan
shaped" pieces of sheet as the basis for the earrings, and you're
going to fuse multiple decorative shapes onto that base, set one
stone in the upper right of one earring and the other in the upper
left of the other earring. Use the fusings, decorative sweat
solders, shape, setting, and other elements to "balance" the pieces
and make it obvious that they are a pair. Tie it together even more
with the pendant, which should echo both earring designs, but be
different in some way on its own.
Another approach is a "moon and stars," where the earrings are
different shapes, but the relationship inherent in the shapes give
meaning to the whole (e.g., one's a moon and one's a star, or one's a
crescent and one's a circle, etc.).
Of course, all this depends on what the client wants and what style
of work you do. If it lends itself to this approach, it can be a
good solution. The human eye won't detect the differences in the
stones very easily because they won't be next to each other, and they
won't be symmetrically placed.