Duchess, the three kitten's mother (white)
Marie, the sister kitten (white)
Berlioz, brother kitten (grey)
Toulouse, brother kitten (orange)
Thomas O'Malley, the three kitten's stepfather (auburn shade of orange with white)

For an orange male kitten and a grey male kitten to show up in the same litter in real life, the mother cat has to be a tortie (black and orange) or a dilute tortie (grey and cream). So for Toulouse and Berlioz to be possible, Duchess would have to be genetically a tortie or dilute tortie under the white fur. The kitten's unknown father or fathers can either be a black based fur color (black or grey) or a red based fur color (orange or cream). Considering that one of the kittens is grey, a dilute color, and the other is orange, a dense color, both mother and father cat or cats would have to carry dilute, but both can't be dilute themselves. Duchess and Marie's all-white fur comes from the dominant white gene, which masks all whatever color fur the cat would have otherwise.

Note: Dominant white gene all-white cats with blue eyes are a little more prone to hereditary deafness than odd-eyed (blue eye and brown/orange/yellow/green eye) all-white cats, brown/orange/yellow/green eyed all-white cats, and white spotting gene all-white cats and cats of any other fur color, blue eyed or not. It is the lack of pigment in the ear that causes deafness and it is polygenes on the dominant white gene that determines this ear lack of pigment.

Duchess, Marie, Toulouse, Berlioz, Thomas O'Malley, and The Aristocats: (c) Disney