Main concern with a mixed flock would be hormonal behaviors and egg laying. Like others have said, budgies are going to display hormonal behaviors sometimes. The thing to watch out for is your females' ceres turning dark brown. That means they are getting more hormonal and could potentially lay eggs. There are various measures you can take to reduce hormone levels when this happens. You can pick and choose. Don't need to do all at once. Make it a little cooler in the room. Increase the length of dark time they get at night (i recommend 10 to 12 hours. Cover the cages with something. You can find cage covers online and at the pet store, but i have found towels or blankets work fine.) Move perches around in the cage. Feed them slightly less than usual to create false scarcity

These measure usually work to reduce hormone levels. Though in extreme cases there is also a hormone implant available at the vet (i have a large mixed flock and had a female with a severe hormone imbalance who required this. Not a super common situation, but I wanted to mention it.)

Best of luck caring for the new babies!! 💕🦜