When selecting a monogram for a couple, the customary way is to combine the initials to create a "blended" monogram.
The monogram style should use the last name initial in the center (the largest letter). For barware and related items, the husband's first name initial is generally first (on the left side). For all other pieces, the wife's first name initial usually appears first (on the left side).
Another simple and attractive option is a single letter monogram, representing the first letter of the couples' last name.
Monogramming For Individuals
Individual monograms may show all initials the same size (first, middle, last)...
The above example shows Benchmark monogram with letter sequence straight selected
Or may feature the last name initial larger, center between the first and middle initials.
The above example shows Benchmark monogram with letter sequence center selected