Brother to sister inbreeding is never a good idea so I would advise not to breed ducklings from a family group together unless you know they are unrelated but hatched out at the same time. We sell ducklings as a straight run and I caution people about keeping both the hens and the drakes together unless they are going to be eating all the eggs and not allowing any to hatch.
Father to daughter and mother to son breedings are considered line breeding and it is okay for one generation but the resulting offspring must be outcrossed. What we have done to grow our flock is to keep hens and swap out the drakes every year. This is the first year we are keeping hens and drakes so we are parting with more hens than usual. We have plenty of hens to run with the drakes so we can keep a good mix of genetics but there will be a slight chance that we get matings between double dilute siblings, which can only produce the dilute color. All ducklings of the double dilute color will have to be outcrossed for future generations so we just have to be cautious about separating ducklings that are the double diluted color.
I think when you have a breeding flock the size of ours, there is a good chance that eggs set together are out of different hens so the ducklings hatched together are not as likely to be direct siblings but the potential is always there so it is better to avoid breeding ducklings hatched together. The fewer breeding adults in the flock, the more likely the ducklings will be too related for breeding.
