Being parasite breeders, it is most important that the host species be happy in the habitat. As these waxbills may be the most numerous birds on earth at this time, the keeper may want to remove their eggs, which are noticeably smaller, to give the best chance to the whydah chicks, at least for the first nest. It is best to have several more pairs of waxbills ready to go to nest than you have hen whydahs. Not all birds will cycle at exactly the same time. It's best to have as many possible nests with broody reds-eared hens waiting as possible.
Male whydahs can be aggressive during mating season.
Therefore, the best results may be obtained from a working colony of waxbills and whydahs only, unless the habitat is exceptionally large. It may also be a good idea to remove the young whydahs when independent, allowing them to mature together.