This one looks like a yellow face opaline greywing.
A rainbow would be clearwing instead of greywing. If the parents were full body greywing rather than normal greywing a true rainbow would be possible. A full body greywing is a combination of greywing and clearwing, it has greywings and bright body colour. It is hard to tell if your pair are full body greywing or normal greywing. The chick in your 2nd picture has light wings like a clearwing but doesn't appear to have bright body colour. The chick in your 4th picture has fairly bright body colour and could possibly be a clearwing with darkish markings