Not to worry, they will be fine... Just keep an eye on them for the next couple of days to a week.
As long as everyone has plenty of space to keep out of each others way for the first couple of days, everyone will find their spot in the pecking order.
I put two week olds with 14 week olds and they acted the same way... real stand-offish from one another for the first couple of days, but eventually they all get a long.
The older ones will put the little ones in their place if they need it, but they will bond and get along perfectly.
With mine, I found that a little white one (named Love Muffin) puts the bigger (older) girls in their place when they try to bully her around.
Love Muffin fights for her spot on the top roost amoungst the big girls and wins 6 out of 7 nights.
It's amazing how the pecking order works in my flock.
Good Luck.