I have ten hens and 3 roos that are about a month older than my ee's and polish. I tried to mix them together a few weeks ago but had to seperate them again. i just let the babies out a day ago. now the babies are much bigger they seem to be getting along just fine. i have a place where the babies can get to if the bigger ones are getting to rough. they are just now starting to eat together drink.
so my suggestion is make sure everyone has enough room to roam so they dont feel over crowded, make a place where the smaller ones can get away from the bigger. if you see that they are not letting them alone, blood, not letting eat, etc seperate them. make sure that you have food and water that is seperate from the big ones, make sure the lil ones are able to eat and drink. i stand in my coop for about 10 mins when i first feed to make sure the lil ones eat and drink what they want. then i leave the coop but watch everyone for awhile.
i know it's scarey when you are seeing them pecking and chasing the lil ones but its normal. make sure you can get to the lil ones if need be fast. also make sure you watch them, check them once or twice every hour all day long. i am no expert but that is what i did and experienced, so far so good for the second time around. hope you and fam are one big happy one soon.