Not sure what you mean by interbreeding?
You can try and breed out the faults by selecting the best offspring of these to breed from (ones which have less white in crest and darkest legs), or you can buy a new better rooster or hen to breed with one of your birds, but tbh I would just get better male and female birds to start with if I was starting a breeding programme, because using your existing birds will take YEARS to breed out the faults.
If you are just doing it for fun and don't care about pure breed standard quality, then just do what you like!
You can try and breed out the faults by selecting the best offspring of these to breed from (ones which have less white in crest and darkest legs), or you can buy a new better rooster or hen to breed with one of your birds, but tbh I would just get better male and female birds to start with if I was starting a breeding programme, because using your existing birds will take YEARS to breed out the faults.
If you are just doing it for fun and don't care about pure breed standard quality, then just do what you like!