You need to separate the drake from the chicks somehow - a pen next to them perhaps - he sees them as a threat and will kill them if he gets the chance. If he and his 'wife' are both khaki campbells he will be extremely possessive of her - KC's are known to be very virile and normally need 8 to 10 females to service.
What are you going to do with the youngsters? You may well have another 6 drakes there
Once you know what sex they are I'd suggest trying to sell them - Gumtree is a possibility - and about £8 to 310 each.