Since we have narrowed down the father to the buff brahma which is gold (s+/s+), the mother has to be Silver. (S/-). Which may be hidden in varieties that show no red/gold unless there is leakage (like your blue cochin rooster, if he was Silver the leakage area should be creamy to white not gold).
This doesn't narrow down the choices much, just eliminates any of your pullets/hens that aren't Silver and can't hide Silver, like the partridge for example.
The Barred cochin (B/-) may also be eliminated if the chick doesn't have Barring, because it would pass the Barring gene to its sons. They would be B/b+.
If that chick is showing Barring then the Barred cochin hen must be its mother, this means she is Silver also.