That's tough, nine 12 week chickens being introduced to two 4 week chickens. Honestly I think they are too small and the established flock is too large for a drop and hope intro. Your setup is good though
I would actually block them off completely like that so the older flock can't get to them, but can see them. Leave them like that for as long as it takes for your established flock to lose some interest (3-4 days or so). Then I would do individual intros starting with the lowest member of your flock.
Establishing pecking order will be some "put in your place" type pecks. When the babies back down or run the higher ranking chicken should kinda puff up and maybe deliver one more to get her point across. If the newbie holds her ground the fight will get more deadly until one backs down. It shouldn't hurt them, just establish who is boss. She generally delivers pecks like that with her head high and a puffed up chest. The lower ranking chicken flattens, lowers her head, or does a quick run backwards - acknowledging she is boss. Watch your bigger flock and you will probably see this because it does continue even after rank is established. Especially with the lead hen - she has to remain lead!
An unacceptance into the flock will be more deadly. The stance of the hen delivering the blows won't necessarily be done with her puffed up tall "regal" posture, just a chase and attack. If the intruder backs down or runs the established hen will go after her. Or, more than one hen will be doing the attack (in a true dominance it is only one at a time - lead hen doesn't want "help" from anybody to do establish dominance, but others are allowed to help when getting rid of an intruder, low ranking especially since this is a way they can prove themselves to the lead). It's not about proving dominance - it's about getting rid of an intruder.
Watch and see what type it is