if you aren't interested in eggs sell the females. people will actually pay ($15-$30 a piece depending on your area) for females but males are tough to give away.
what temperature is the brooder? is there plenty of food and water? is there anything in the brooder that is being heated by the lamp and giving off fumes?
breeding is only bad if it is done without a purpose. if your purpose is eggs and meat then hybrids can work great because "hybrid vigour" can result in offspring that produce more eggs than either parent strain and/or grow faster resulting in more efficient meat produciton.
looks like you haven't posted in a while but wanted to ask if you could share photos of the appleyard/harlequin crosses. curious what they look like because the parents have so many similar qualities. i bet they are great layers!
curious do you have any photos of the mature GC drake? and the SA/GC crosses (both as ducklings and mature)? i imagine those crosses make great layers!
based on my research holderread currently only sells and ships goslings of these 4 breeds: dewlap toulouse, embden, dewlap african (brown and buff), american (blue and lavender)
my extremely novice guess based on pictures on the holderread website (and zero hands on experience) is #1 are...