I was never in a situation where my chicks would out of the blue want to attack their father when he got near them. And this is especially true when the father has never displayed a violent attitude towards them.
These chicks could be copying the mother's behaviour, they have seen and suffered abuse from her.
During this time, it's vital to keep a closer watch on the interactions between the chicks and the father, once they are hungry and start to beg, the father will feel encouraged to feed them. He has been with them since day 1 and has supported the mother and them up until now, the chicks should recognize him as their father.
If the older chicks continue to show hostility toward their father, and they aren't getting enough food on their crops, then it will be up to you to help them out and give them a boost.
During socialization/bonding time, you can turn their play area into a small feeding station with plenty of egg food, spray millet, soft veggies and their seed mix/pellets. To help the chicks to practice dehusking the seeds, you can get them a seed mix for finches, this will contain basically the same seeds in a budgie seed mix, only they are smaller in size and easier for weaning chicks to eat.
At this stage, even your youngest chick can be encourage to eat these foods, especially when he/she sees their older siblings trying the food out.
Despite this, the chicks (especially the youngest) will need supplemental feedings if the father doesn't fulfil his role.
This link here should be helpful: https://talkbudgies.com/budgie-breedi...ing-guide.html
You can read this one too for extra info on chick aggression
Best of luck with everything!