By "moths" do you mean moth larvae, as the moths themselves feed from flowers.
Whether they are Cabbage Moth larvae or the larvae of white butterflies you can keep them off your plants by using fine mesh over them, stretched taut so there is no way in, especially at ground level. It can look neat and tidy, not hideous.
Both only lay their eggs on plants of the cabbage family ie Brassicas so will not infest other plants, so no worries there, even if this year it is a little late to protect your cabbages.. always next season!
The yellow "buds" on your kale do sound like butterfly eggs: kale is a brassica so perhaps you could grow these under the same net as cabbages next time around? In the meanwhile ask your brother to keep a look out for any chewed leaves and capture the culprit caterpillar, which will be small and green, well camouflaged, probably sitting cosliy along a leaf vein.
I hope that helps a bit