Chick 2 had fledged when I went up today. She also had the bloodied face of a fledged Red Rump When I opened the nest box to check on the others Chick 1 jumped out of the box and started flying around (and crashing LOL).
Chick 1 with some of the other residents:
Chick 4 looks like he's going to be a cheeky boy! His colouring is a normal red rump which is confusing: