The marriage of the two sisters is married.

The sentence “The marriage of the two sisters is married” is better phrased as “Each of the two sisters is married,” using “each” to emphasize individual status. In English, “each” is used for individual members of a small group, fitting the context of two sisters. Options A (both, implying collective), C (all, for larger groups), and D (either, for one of two) do not convey the individual focus as accurately, making B correct.