Without a mama to protect them, I'd wait until they were fully feathered...maybe 4 weeks...before integrating. If you free range daylight to dark, you can integrate pretty easily by just letting them out on the range in the morning and watching how the flock reacts. They can easily evade any cranky hens and the roo probably won't give them a second look...or he may just take them under his wing and protect them~I've seen both reactions.
If it looks like they are getting the wrong end of the action, just keep something handy under which they can duck but the bigger birds cannot so they can get away and regroup(piece of plywood or some such up on bricks). Come evening they will all go in the coop and the bigger birds will get up on the roosts and the smaller will bed down on the floor and all will be well. There might be issues at the feeder but the younger birds will learn real fast to avoid trying to eat first.