I am another for suggesting the baby monitor. One tip is try not to have it RIGHT near their beds because every little sniffle, snore, wriggle will be picked up. Try it on the other side of their room. It's like someone on a PA system next to your bed if put too close to them! I was petrified when DD actually slept in her cot that I wouldn't hear her wake and only used the monitor for one night. It was so damn loud lol. She's literally only 5 meters away though.

HTH and GL transitioning them hun!