What type of quail do you have? And are the existing quail adults? When mixing adults with juveniles, I have found that mixing my Bobwhites in my aviaries can be done with little aggression if done right. And especially this time of year, if you don't have lights on your quail and they are not in breeding mode there is less aggression with the existing quail.
But what I do is, get one or more, depending on how many quail you are introducing, of those extra large dog crates, the metal barred kind, and put the new quail in there in the aviary. Leave the new ones in the crates for a few weeks or even several weeks so that everybody sees each other and can get used to each other from behind the bars. When a few weeks have past, let one or a few out and see what happens. Watch them all very closely for several days as fighting can ensue days later. Don't ignore simple chases and make sure it does not escalate into bloody matches. Being that they have been living with each other for so long now, there shouldn't be too much fighting.
If one or more of your existing quail are fighting badly with the new ones, put those aggressive ones in these cages and keep THEM separated for a few weeks. Generally this will pipe the aggressors down and eventually you can mix them all. Keep the cage handy for a while for "time outs" on any aggressive quail.
If you are mixing juveniles with other younger quail, it can be done this way, however they may require less time in the cages as it is the older quail that are more aggressive than young quail. Good luck!