I would say that taking them to a groomer to have their wings clipped would be the best solution. That way, if they get startled by a loud noise, they will be least likely to try to fly into a wall, or worse. Clipping a bird's wings is a common method for keeping birds from flying around until they're used to their new home, making them fully dependent on their owner.
If it's done correctly, wing clipping doesn't hurt the bird, although it will generally look a bit unruly. Since clipping the bird's wings removes their ability to fly, it also removes their ability to exercise. I suggest that you don't continue to clip the bird's wings after they are comfortable living with you, when the risk of them flying away is gone. You'll have a much happier and healthier bird in the long run.
If you want to clip the bird's wings yourself, I suggest using the standard cut. There are other cuts that are intended to make the wing look "attractive", but generally it's best to leave those cuts to professionals as you don't want to cut the pin feathers (sometimes referred to as blood feathers).
Here's an article that gives a pretty good overview of what wing clipping is, and why bird owners decide to do it. They also suggested the use of a bird harness, which is another good option if you're not comfortable with having their wings clipped.
Everything else really just takes time. Try not to cause them unneeded stress, and don't try to handle them too much for the first couple days. It's also a good idea to try to keep the house fairly quiet, or at least avoid making startling noises or movements around them. In time, they'll be used to their new home and associate you with food.