Wouldn't there be more gold leakage from that cross, assuming the dominant white gene wasn't passed down? It's difficult to know for sure what the color genetics are for Cookie and Cream and Smokey Pearls, so that complicates things a lot. But I agree that the barred rock and Cochins aren't contenders.Both ISA browns and smokey pearls are hybrids that should be heterozygous dominant white, so would have a 50-50 shot of passing the gene on. A chick not inheriting the gene does not rule out either of them as the mother, in other words. From a Black Australorp, I would expect less color leaking through, especially this early on, personally. But, it could still be possible, which is why I didn't rule her out entirely.
Personally, based on how widespread the color leaking is on him, I'd lean the most toward the ISA as the mother. Their genetics tend to impart a lot of color leaking in mixes out of them.