Dead chicks

Found 3 dead chicks on the aviary floor. The Hecks have thrown out their newly hatched chicks, I don't know why. Could have been the recent cold spell, or not fed properly..there was no sign of any food in their crops. Don't know...bird keeping can be very frustrating!
To add to the problems, Barney has got something wrong with him. It's like he's had a stroke. His right foot is not gripping and his left wing is hanging. He can still fly, but he's struggling. He is my best bird and never shown any signs of illness before.