I'm thinking of taking them back to only full modern and other 50\50 crosses not full sebright again so maybe could stay clear from that, they're parents were black birchen cock over gold sebright hen and I'm about to produce some from bb red cock over silver sebright hens then take the two broods together while introducing full modern here and there for the leg and frameYou got some work ahead to breed out the reproductive problems coming from the sebright side.