Who is The Count and Countess Andrenyi from Murder on the Orient Express and what is their importance?

The Count and Countess are described as worldly, sophisticated, exotic, gracious, and under the murderous circumstances, a bit bewildered. In reality, however, the Countess is actually Mrs. Armstrong's sister and Mrs. Hubbard's daughter.

The Count is exactly who he claims to be..... he does, however, cover for his wife.