Mum is trying her best !

At first I thought the mum had been taken but as the remaining bird is spending the nights in the nest, it must have been the dad.
Mum is working hard to keep the chicks fed but it is a relentless task, as I am sure it would be for 2 adults, let alone 1.
We do have 4 chicks stronger than the other 2 which now means the other 2 are pushed to the bottom/back where they get little food if any. This then causes them to be weak and not develop as much, which gets them in a catch-22 situation.
Not sure if we can do anything to help. We have bought some meal worms to try and help the mum get some food quickly to more chicks but we cant find a good place to put them where they will be taken by our birds, and not all the others in the garden!