I have had EXCELLENT luck by allowing the grown flock to SEE and HEAR the baby chicks (while the chicks are in their brooder) from the time they come onto your property until the day that you fully incorporate them into the flock at the age of 6 to 7 weeks. This is often called the "see but don't touch" method of integrating birds into an existing flock. Ensure that you have plenty of space for your babies to duck under that the adults cannot reach them and place food and water in that safe area for them. By incorporating them LONG before they're fully grown, they are perceived as a non-threat and will incorporate much easier; often in less than one week you will see them accepted into the flock. Best of luck with your rooster and the hen that he either doesn't like (or that doesn't like HIM).