There will be some squabbles whenever you do it. The safest time is after the chicks are adult size -- but you can try it now if you wish. The mama might do a good job of protecting her chicks. I would certainly have a big area to put them together in, with hiding places available. You could even fix up a small space where the chicks could go if necessary, with an opening too small for the adults, although they will want to stay close to their mama. Also have some treats handy.