At 9-10 weeks nobody will be concerned about the roosters. Chickens are very territorial and will resent all the new ones. You may have some softies and they don`t care about the new additions, but often that is not the case. If your older cockeral was mature, as in over a year, he wouldn`t be a threat to them at all, but hens, the pullets, and a young cockeral will need watching. It`s good you have plenty of room for them to escape, but you still need to be aware that conflicts may occure. Good luck.........Pop